A cold is a respiratory infection caused by one of hundreds of possible viruses. However, because these viruses are so widespread, it is perhaps more accurate to say that colds are caused by a decrease in immunity that allows one of these viruses to take hold.

Colds occur more frequently in winter, but no one knows exactly why. Nearly everyone catches colds occasionally, but some people catch colds quite frequently, and others tend to stay sick an unusually long time.

Influenza B, commonly called the flu, occurs in the form of a worldwide epidemic every winter. The predominant symptoms of flu are fever, malaise, and muscle aches. Cold-like respiratory symptoms are usually fairly minor with the flu. However, a dangerous type of pneumonia can develop as a complication of influenza, especially in seniors.

Conventional medicine can neither cure nor prevent the common cold. Furthermore, none of the over-the-counter treatments have been found to shorten the duration of a cold or even provide significant temporary relief. Cough syrup, in fact, seems to be no better than placebo.111-112 Some of the natural treatments described in this section may be able to do better.

People often want to take antibiotics for colds, and many physicians will prescribe them—even though antibiotics have no effect on viruses. Many believe that when the mucus turns yellow, it means that a bacterial infection has occurred for which antibiotic treatment is indicated. However, viruses can also produce yellow mucus and even if bacteria have made a home in the excess mucus, they may be only innocent bystanders and produce no symptoms.

Colds, however, can be complicated by bacterial infections. In such cases, antibiotic treatment may be indicated.

The situation is somewhat better for influenza. The “flu shot” provides protection against several strains of influenza. There are also prescription antiviral medications that can help prevent flu and also reduce its length and severity if you do come down with it.

Principal Proposed Natural Treatments

Various natural treatments have shown promise for treating or preventing colds, which are described below. See also the treatments discussed in the Acute Bronchitis article.

One famous alternative treatment for colds is the use of zinc in nasal gel or lozenges. When you take zinc this way, you are not using it as a nutrient. Rather, certain forms of zinc release ions that are thought to directly inhibit viruses in the nose and throat.

Taking zinc orally as a nutrient might also be useful in some cases. The immune system does not function properly if you do not have enough zinc in your body.1-2 Because zinc is commonly deficient in the diet, especially among children and senior citizens,3 nutritional zinc supplementation may certainly be useful for those who get sick easily. A 1-year, double-blind study of 50 nursing home residents found that zinc supplements as compared to placebo reduced rates of infection.159 In addition, more than ten other studies performed in developing countries have found that zinc supplements at nutritional doses can increase resistance to respiratory and other infection in children, and that they might reduce symptom severity.5-6,157,165

In a review of 17 randomized trials with 2,121 patients, oral zinc started within 3 days of cold symptom appearance showed mixed results when compared to placebo or no treatment. Four trials with 412 patients showed no significant decrease in symptom severity. However, the risk of being symptomatic after 7 days was reduced significantly in 9 trials with 1,325 patients. Cold symptoms were reduced by an average of 2.6 days in an analysis of 5 trials with 371 adults. No significant differences in cold symptom duration were found in 3 trials with 563 children.181

Note: With zinc, more is not better; once you do have enough zinc, getting extra will not help, and might even hurt.

Use of lozenges containing zinc gluconate or zinc acetate have shown somewhat inconsistent but generally positive results for reducing the severity and duration of the common cold. For example, in a double-blind trial, 100 people who were experiencing the early symptoms of a cold were given a lozenge that either contained 13.3 mg of zinc from zinc gluconate or a placebo.8 Participants took the lozenges several times daily until their cold symptoms subsided. The results were impressive. Coughing disappeared within 2.2 days in the treated group versus 4 days in the placebo group. Sore throat disappeared after 1 day versus 3 days in the placebo group, nasal drainage in 4 days (versus 7 days), and headache in 2 days (versus 3 days). Positive results have also been seen in double-blind studies of zinc acetate.9,10,167 While not all studies have been supportive,11 on balance, results appear to favor the effectiveness of zinc lozenges for treating symptoms of the common cold.12,143,174

It has been suggested that the exact formulation of the zinc lozenge plays a significant role in its effectiveness.13 According to this view, certain flavoring agents, such as citric acid and tartaric acid, might prevent zinc from inhibiting viruses. In addition, chemical forms of zinc other than zinc gluconate or zinc acetate might be ineffective. Zinc sulfate in particular might not work. Along the same lines, sweeteners such as sorbitol, sucrose, dextrose, and mannitol are said to be fine, while glycine has been discussed in an equivocal manner.

Use of zinc in the nose is somewhat more controversial.144 In addition to showing inconsistent results in studies, use of zinc nasal gel can cause pain and possibly loss of sense of smell.

In one double-blind, placebo-controlled trial, 213 people with a newly starting cold used one squirt of zinc gluconate gel or placebo gel in each nostril every 4 hours while awake.7 The results were significant: treated participants stayed sick an average of 2.3 days, while those receiving placebo were sick for an average of 9 days, a 75% reduction in the duration of symptoms. Somewhat more modest but still significant relative benefits were seen with zinc nasal gel in a double-blind, placebo-controlled study of 80 people with colds.103 However, a slightly larger study of a similar zinc gluconate nasal gel found no benefit.113 Another study—this one involving 77 people—failed to find benefit, even with near constant saturation of the nasal passages with zinc gluconate nasal spray.144

Other than its direct affect on viruses during an infection, zinc supplements (not lozenges) may play a role in reducing the risk of coming down with a cold in the first place. In a review of 2 randomized trials, which included 394 healthy children, researchers found that the groups who took zinc had fewer colds, school absences, and prescriptions for antibiotics.174

For more information, including dosage and safety issues, see the full Zinc article.

Until the 1930s, echinacea was the number one cold and flu remedy in the United States. It lost its popularity with the arrival of sulfa antibiotics. Ironically, sulfa antibiotics are as ineffective against colds as any other antibiotic, while echinacea does seem to be at least somewhat helpful. In Germany, echinacea remains the main remedy for minor respiratory infections.

Echinacea is generally thought to work by temporarily stimulating the immune system, although most (but not all) recent evidence has tended to cast doubt on this belief.104-105, 145-146 Contrary to popular belief, however, there is little reason to believe that echinacea strengthens or "nourishes" the immune system when taken over the long term.

There are three main species of echinacea: Echinacea purpurea, Echinacea angustifolia, and Echinacea pallida. A mixture containing all the parts of E purpurea above the ground (flowers, leaves, stems) has the best supporting evidence for effectiveness in treating colds and flus;147 the root of E. purpurea is probably not effective, while the root of E. pallida may be the active part of that species.

Echinacea has shown promise for reducing the symptoms and duration of colds and aborting a cold once it has started. However, echinacea does not appear to be helpful for preventing colds. It may also not be effective in children.

Double-blind, placebo-controlled studies enrolling a total of more than 1,000 people have found that various forms and species of echinacea can reduce the symptoms and duration of a common cold, at least in adults.14-21,115,145 The best evidence is for products that include the above-ground portion of E. purpurea rather than the root.

For example, in one double-blind, placebo-controlled trial, 80 individuals with early cold symptoms were given either E. purpurea extract or placebo.22 The results showed that individuals who were given echinacea recovered significantly more quickly: in just 6 days among the echinacea group versus 9 days among the placebo group. An in another double-blind trial, researchers found a reduction in symptoms with E. purpurea compared to placebo among 282 cold sufferers.115

Another double-blind, placebo-controlled trial looked at reduction of the severity of cold symptoms.23 The results in 246 participants showed that treatment with E. purpurea significantly improved cold symptoms such as runny nose, sore throat, sneezing, and fatigue. Symptom reduction with E. purpurea was also seen in a double-blind, placebo-controlled study of 282 people.115

In addition, three double-blind, placebo-controlled studies enrolling a total of about 600 participants found similar benefits with a combination product containing E. purpurea and E. pallida root, along with wild indigo and white pine.106-107,140-141

While the above evidence tends to suggest that the above-ground portion of E. purpurea is active against the common cold, two studies have failed to find benefit. One of these was a double-blind, placebo-controlled study enrolling 120 adults,116 the other an even larger trial (407 participants) involving children.117 The reason for these negative outcomes is not clear. E. angustifolia root has also failed to prove effective in a large study.148E. angustifolia root has also failed to prove effective in a large study.148

Studies investigating the root portion of E. purpurea have been less supportive. In one trial, for example, 246 individuals with recent onset of a respiratory infection were given either placebo or one of three E. purpurea preparations: two formulations of a product made of 95% above-ground herb (leaves, stems, and flowers) and 5% root, and one made only from the roots of the plant.23 The results showed significant improvements in symptoms with the above-ground preparations, but the root preparation was not effective. And, in a large, randomized study, researchers found that dried echinacea root (10.2 grams for the first 24 hours of a cold and 5.1 grams for the next 4 days) did not improve symptoms more than placebo or no treatment.173

A double-blind study suggests that echinacea can not only make colds shorter and less severe, it might also be able to stop a cold that is just starting.24 In this study, 120 people were given E. purpurea or a placebo as soon as they started showing signs of getting a cold.

Participants took either echinacea or placebo at a dosage of 20 drops every 2 hours for 1 day, then 20 drops 3 times a day for a total of up to 10 days of treatment. The results were promising. Fewer people in the echinacea group felt that their initial symptoms actually developed into "real" colds (40% of those taking echinacea versus 60% taking the placebo actually became ill). Also, among those who did come down with "real" colds, improvement in the symptoms started sooner in the echinacea group (4 days instead of 8 days). Both of these results were statistically significant.

Several studies have attempted to discover whether the daily use of echinacea can prevent colds from even starting, but the results have not been promising.

In one double-blind, placebo-controlled trial, 302 healthy volunteers were given an alcohol tincture containing either E. purpurea root, E. angustifolia root, or placebo for 12 weeks.25 The results showed that E. purpurea was associated with perhaps a 20% decrease in the number of people who got sick, and E. angustifolia with a 10% decrease. However, the difference was not statistically significant. This means that the benefit, if any, was so small that it could have been due to chance alone.

Another double-blind, placebo-controlled study enrolled 109 individuals with a history of four or more colds during the previous year and gave them either E. purpurea juice or placebo for a period of 8 weeks.26 No benefits were seen in the frequency, duration, or severity of colds. ( Note: This paper is actually a more detailed look at a 1992 study widely misreported as providing evidence of benefit.27)

Four other studies also failed to find statistically significant preventive effects.90,91,118,169

A study often cited as evidence that echinacea can prevent colds actually found no benefit in the 609 participants taken on whole.92 Only by looking at subgroups of participants (a statistically questionable procedure) could researchers find any evidence of benefit, and it was still slight.

However, a recent study using a combination product containing echinacea, propolis, and vitamin C did find preventive benefits.119 In this double-blind, placebo-controlled study, 430 children ages 1 to 5 years were given either the combination or placebo for 3 months during the winter. The results showed a statistically significant reduction in frequency of respiratory infections. It is not clear which of the components of this mixture was responsible for the apparent benefits seen.

For more information, including dosage and safety issues, see the full Echinacea article.

Andrographis is a shrub found throughout India and other Asian countries, sometimes called Indian echinacea because it is believed to provide much the same benefits. It has been used historically in epidemics, including the Indian flu epidemic in 1919, during which andrographis was credited with stopping the spread of the disease.36 Recently, it has become popular in Scandinavia as a treatment for colds.

Although we do not know how andrographis might work for colds, some evidence suggests that it might stimulate immunity.37 Interestingly, the ingredient of andrographis used for standardization purposes, andrographolide, does not appear to affect the immune system as much as the whole plant extract.

According to a few, well-designed studies (almost all of which used the proprietary extract produced by a single company), andrographis can reduce the symptoms of colds. It may offer the additional useful benefit of helping to prevent colds.

A total of seven double-blind, placebo-controlled studies enrolling, all together, almost a 1,000 people have found that andrographis (or a combination containing it as the presumed primary ingredient) significantly reduces the duration and severity of cold symptoms.38-40,120,

For example, a 4-day, double-blind, placebo-controlled trial of 158 adults with colds found that treatment with a proprietary andrographis extract significantly reduced cold symptoms.41 Participants were given either placebo or 1,200 mg daily of an andrographis extract standardized to contain 5% andrographolide. The results showed that by day 2 of treatment, and even more by day 4, individuals given the actual treatment experienced significant improvements in symptoms as compared to participants in the placebo group. The greatest response was seen in earache, sleeplessness, nasal drainage, and sore throat, but other cold symptoms improved as well.

Three other double-blind, placebo-controlled studies, enrolling a total of about 400 people, evaluated a proprietary herbal combination treatment containing both andrographis and Eleutherococcus senticosus (so-called Russian Ginseng) and found benefit.42,108 Another study suggests that this combination may be more effective than echinacea.121 (Somewhat confusingly, this proprietary combination is sold under the same name, “Kan Jang,” as the pure andrographis product noted above; the manufacturer regards this combination as more effective than andrographis alone, and the combination version of the product has now superseded the previous single-herb version.)

The same combination has also shown promise in two double-blind studies for reducing the duration, severity, and rate of complications of influenza.122

Andrographis has also been compared to acetaminophen (Tylenol). In a double-blind study of 152 adults with sore throat and fever, participants received andrographis (in doses of 3 g or 6 g per day for 7 days) or acetaminophen.43 The higher dose of andrographis (6 g) decreased symptoms of fever and throat pain to about the same extent as acetaminophen, but the lower dose of andrographis (3 g) was not as effective. There were no significant side effects in either group. This study used a different form of andrographis than the proprietary product noted above.

According to one double-blind, placebo-controlled study, andrographis may increase resistance to colds.44 A total of 107 students, all 18 years old, participated in this 3-month trial that used the same proprietary extract of andrographis noted earlier. Fifty-four of the participants took two 100 mg tablets standardized to 5.6% andrographolide daily—considerably less than the 1,200 mg to 6,000 mg per day that has been used in studies on treatment of colds. The other 53 students were given placebo tablets with a coating identical to the treatment. Then, once a week throughout the study, a clinician evaluated all the participants for cold symptoms.

By the end of the trial, only 16 people in the group using andrographis had experienced colds, compared to 33 of the placebo-group participants. This difference was statistically significant, indicating that andrographis reduces the risk of catching a cold by a factor of two as compared to placebo.

For more information, including dosage and safety issues, see the full Andrographis article.

Vitamin C may mildly reduce symptoms of colds when they occur, but it probably does not help prevent colds.

Numerous studies have found that vitamin C supplements taken at a dose of 1,000 mg or more daily can reduce the severity cold symptoms and shorten their duration. However, the effect is modest at best .50,51,100,172 In addition, at least one study suggests that vitamin C can enhance the effect of standard cold treatments, such as acetaminophen.109 According to most of these studies, using vitamin C throughout the cold season, rather than intermittent, appears to be beneficial. For example, a review of 29 placebo-controlled trials involving almost 1,000 episodes of illness concluded that taking at least 2,000 mg per day preventively seems to result in shorter and less severe colds when they occur. .172 However, high doses of vitamin C does not appear capable of decreasing the number of colds experienced during a season.

But, many people use vitamin C for colds in a different way: they only begin taking it after cold symptoms first appear. In a review of 7 randomized and non-randomized trials, researchers found that this approach—taking high doses of vitamin C (eg, 2,000 - 4,000 mg) at the first sign of illness—does not seem to affect the cold's severity or duration.172

Although some studies suggest that regular use of vitamin C throughout the cold season can help prevent colds,100,149 most other studies have found little to no benefit along these lines.99

Vitamin C has shown a bit more promise for prevention of one type of cold, the post-marathon sniffle. These are colds that develop after endurance exercise; use of vitamin C before and during competition may help keep you cold-free afterwards.54,55 In addition, vitamin C seems to help prevent respiratory infections among individuals who are actually deficient in the vitamin.56

For more information, including dosage and safety issues, see the full Vitamin C article.

Eucalyptus is a standard ingredient in cough drops and in oils meant to be added to humidifiers. A standardized combination of three essential oils has been tested for its usefulness in respiratory conditions. The studied combination, called essential oil monoterpenes, includes cineole from eucalyptus, d-limonene from citrus fruit, and alpha-pinene from pine. Numerous double-blind trials have found them effective when taken orally for acute bronchitis, chronic bronchitis, sinus infections, and other respiratory conditions, in both adults and children.68-72,101 Cineole alone at a dose of 200 mg three times daily showed benefit in a double-blind, placebo-controlled study of 152 people with cold symptoms.150 And a second study involving 150 subjects also demonstrated favorable results of cineole compared to a combination of five other herbal products.168

Researchers have also investigated the potential benefits of pairing eucalyptus with cayenne. A small randomized, placebo-controlled trial involving 42 people with nonallergic rhinitis found that a product called Sinus Buster (an intranasal spray that contains cayenne and eucalyptus) used twice daily for 2 weeks helped to improve sinus congestion, pain, pressure, and headache.180

Eucalyptus oil is also one of the ingredients found in vapor rub (eg, Vicks VapoRub), an ointment that is applied to the throat and chest to help with congestion as a form of aromatherapy. In one trial, 138 children (aged 2-11 years old) with upper respiratory infection were randomized to receive vapor rub (camphor, menthol, and eucalyptus oils), petroleum jelly, or no treatment.175 The children who had vapor rub applied before bedtime experienced an improvement in their nighttime symptoms (eg, less coughing, less nasal congestion) compared to the other two groups.

For more information, including dosage and safety issues, see the full Eucalyptus and Essential Oil Monoterpenes articles.

Although most people in the West think of ginseng as a stimulant, in Eastern Europe ginseng is widely believed to improve overall immunity to illness. As we have seen, echinacea does not seem to prevent respiratory infections. But it appears that regular use of ginseng might be able to provide this important benefit.

There are three different herbs commonly called ginseng: Asian or Korean ginseng ( Panax ginseng), American ginseng ( Panax quinquefolius), and Siberian "ginseng" ( Eleutherococcus senticosus). The latter herb, which is not discussed here, is actually not ginseng.

A double-blind, placebo-controlled study of 323 people found meaningful evidence that an extract of American ginseng taken at 400 mg daily may help prevent the common cold.151 Participants who used the extract over 4 months experienced a reduced number of colds as compared to those taking the placebo. Comparative benefits were also seen regarding the percentage of participants who developed two or more colds, and the severity and duration of cold symptoms that did develop. Similar benefits were also seen in a study of 43 people.152

Two double-blind, placebo-controlled studies enrolling a total of about 100 people indicate that American ginseng may also help prevent flu-like illness in seniors.123

For more information, including dosage and safety issues, see the full Ginseng article.

The herb garlic has a long history of use for treating or preventing colds. However, up until 2001, there was no scientific evidence that it actually works for this purpose. In fact, many people joked that garlic merely makes you smell so bad people stay away from you, and so you do not catch their cold.

However, there is now some evidence that garlic may really work.

In one 12-week, double-blind, placebo-controlled trial, 146 individuals received either placebo or a garlic extract between November and February.96

The results showed that participants receiving garlic were almost two-thirds less likely to catch cold than those receiving placebo. Furthermore, participants who did catch cold recovered about one day faster in the garlic group as compared to the placebo group.

Benefits were also seen in a smaller double-blind study.124

Note that these studies do not indicate that taking garlic will help once you already have a cold.

For more information, including dosage and safety issues, see the full Garlic article.

Probiotics are healthy organisms that colonize the digestive tract. Not only can they help preventive intestinal infections, they appear to help prevent colds as well.

A 7-month, double-blind, placebo-controlled study of 571 children in day care centers in Finland found that use of milk fortified with the probiotic bacteria Lactobacillus GG modestly reduced the number and severity of respiratory infections.73 In another controlled trial, probiotics ( Lactobacillus rhamnosus GG and Bifidobacterium lactis Bb-12) given daily to infants in their formula significantly reduced the risk of acute otitis media and recurrent respiratory infections during the first year of life compared to placebo.170

Benefits were also seen in three other large studies, in which probiotics alone or combined with multivitamins and minerals helped prevent colds and/or reduce their duration and severity in adults.153-155

Another controlled trial involving 20 healthy elite distance runners found that Lactobacillus fermentum given over a 4-month period during winter training was significantly more effective at reducing the number and severity of respiratory symptoms than a placebo.166

In addition, a small double-blind study found evidence that use of the probiotic bacteria Lactobacillus fermentum improved the effectiveness of the influenza vaccine.158 The probiotic supplement was taken in two doses: one, two weeks before the vaccine, and the other, two weeks after.

A review of 13 randomized trials with 3,780 children, adults, and older adults compared different probiotics to either placebo or no treatment for prevention of colds. Probiotic use was associated with lower risk of number of colds and shorter duration of cold. Several types of probiotics were used in the trials, including:182

  • Actimel with L. paracasei (L. casei), Streptococcus thermophilus, and Lactobacillus bulgaricus
  • L. plantarum HEAL 9 plus L. paracasei 8700:2
  • Lactobacillus rhamnosus strain GG
  • L. rhamnosus plus Bifidobacterium lactis Bb-12
  • Lactobacillus acidophilus plus Bifidobacterium bifidum
  • L. acidophilus plus L. casei

For more information on these “friendly bacteria," see the full Probiotic article.

Other Proposed Natural Treatments

Various other natural treatments have shown some promise for preventing or treating colds and flus.

Use of multivitamin/multimineral supplements, or supplements containing zinc and selenium alone, may help prevent respiratory infections in elderly individuals, according to some but not all studies.4,93,98,125,131-132 However, serious concerns have been raised that one of the researchers involved in studying this topic might have engaged in questionable scientific practices.

One small double-blind study suggests that the supplement arginine might be helpful for preventing colds in children.77

A gargle made from green tea extract has shown promise for preventing influenza.156 In a double-blind, placebo-controlled study, 124 residents of a Japanese nursing home gargled with green tea catechins or placebo for three months. All participants received standard influenza vaccine. The results showed that residents who gargled with the tea extract were less likely to develop influenza than those using the placebo. In addition, another double-blind study found preliminary evidence that oral consumption of a green tea extract might help prevent both colds and flus.163

There is some evidence that the supplement glutamine may, like vitamin C, help prevent post-exercise infections.78-83 For example, a double-blind, placebo-controlled study evaluated the benefits of supplemental glutamine (5 g) taken at the end of exercise in 151 endurance athletes.84 The result showed a significant decrease in infections among treated athletes. Only 19% of the athletes taking glutamine got sick, as compared to 51% of those on placebo. Echinacea has also shown a bit of promise for this purpose.160

In contrast, some evidence suggests that a combination of vitamin E and beta-carotene treatment might increase risk of exercise-associated colds.126 The evidence regarding whether vitamin E taken alone can prevent respiratory infections is conflicting.102, 134

A randomized, placebo-controlled trial involving 164 men (aged 18-28) found that taking vitamin D3 (400 units daily for 6 months) may prevent respiratory infections.177 But, there was no evidence that the vitamin decreased sick days or severity of cold symptoms. Similar results were found in a trial of 322 healthy adults who took vitamin D3 for 18 months. There were no differences in the amount of colds or their severity.183

The thymus gland plays a role in immunity. A 1-year, double-blind, placebo-controlled trial of 16 children with frequent respiratory infections found that treatment with thymus extract could reduce the rate of infection.85 However, a double-blind, placebo-controlled trial of 60 athletes failed to find any significant evidence of benefit with thymus extract for preventing post-exercise infections.86

An extract of rice bran has shown some promise for preventing or treating colds in seniors.133

A throat spray made from sage has shown considerable promise for reducing sore throat pain.135

A study widely reported as showing that the supplement colostrum can help prevent colds was actually far too preliminary to prove anything at all.127

There is some evidence that elements in kelp might help to prevent infection with several kinds of viruses, including influenza.87 However, the evidence thus far is more theoretical than practical.

Various herbs are said to enhance immunity over the long term, including ashwagandha, astragalus, garlic, maitake, reishi, and suma. However, there is as yet no meaningful evidence that they really work. In addition, several herbs, including ginger, kudzu, osha, and yarrow, are said to help avert colds when taken at the first sign of infection; but again, there is no scientific evidence that they are effective.

Products containing colloidal silver are sometimes used in the belief that they will prevent colds and otherwise strengthen the immune system; however, because colloidal silver can cause permanent color changes in the skin, we recommend that you do not use it.88

Some seniors do not respond fully to the influenza vaccine. There is some evidence that vitamin E supplements may strengthen the immune response to vaccinations.74 Similarly, evidence from two double-blind trials,93,94 but not a third,102 suggests that combined multivitamin/multimineral supplements may improve their response. However, in another trial, a multivitamin tablet without minerals actually worsened participants' response to the vaccine.95

Two studies suggest that combined multivitamin/multimineral supplements can also improve immune response to the vaccine.93,94 However, two others failed to find benefit,102,128 and in one study a multivitamin tablet without minerals actually worsened participants' responses to the vaccine.95 The reason for these discrepancies is unclear; however, serious concerns have been raised that one of the scientists who reported benefits in some of these trials engaged in questionable scientific practices.

In a double-blind, placebo-controlled study of 124 people, the supplement chlorella at a dose of 200 mg or 400 mg daily failed to enhance response to influenza vaccine.129

Another study failed to find benefit with a remedy from Traditional Chinese Herbal Medicine, Hochu-ekki-to.136

A standardized product containing elderberry combined with small amounts of echinacea and bee propolis has been widely marketed as a cold and flu remedy. Weak evidence suggests that this mixture may stimulate the immune system and also inhibit viral growth.75 In a preliminary double-blind study, the combination significantly reduced the recovery time from epidemic influenza B (a relatively mild form of influenza).76 Another small double-blind study found similar benefits in both influenza A and B.130

Honey has also been studied as a potential treatment for the symptoms of upper respiratory infections, especially nighttime cough.178,179 In one study, 130 children aged 2-17 with runny nose and cough were randomized to receive nightly doses of buckwheat honey, artificial honey-flavored cough medicine (dextromethorphan), or no treatment.178 On a parent-rated symptom scale, honey was found to be the most helpful in reducing nighttime cough and improving sleep in children with upper respiratory infection. Adding to these positive results, another study randomized 139 children aged 2-5 years old with upper respiratory infection to 1 of 4 treatment groups: honey, dextromethorphan, diphenhydramine (eg, Benadryl), or no treatment.179 Standard care, such as acetaminophen and nose drops, was also given to all children as needed. While improvement was seen in all of the groups, children receiving honey had the fewest episodes of nighttime cough and slept better compared to children in the other groups.

One small study found that the "Throat Coat" brand of medicinal beverage teas actually does reduce sore throat discomfort, as compared to placebo tea.137

Inhaled essential oils have shown a slight bit of promise for the treatment of colds.110

The herb pelargonium sidoides is used in Europe for the treatment of colds and other respiratory infections.138 A double-blind study of 133 adults who had just come down with the common cold found that use of a standardized pelargonium extract taken at a dose of 30 ml three times daily significantly reduced the severity and duration of symptoms as compared to placebo.164

In double-blind, placebo controlled studies enrolling a total of over 300 people, a combination of four herbs (primrose, gentian root, elderberry, common sorrel, and vervain) has shown promise for treatment of sinusitis.139

One study provides weak evidence that a standardized combination of horseradish and nasturtium might be helpful for the treatment of the common cold in children.162

Other herbs sometimes recommended to reduce cold symptoms, but that lack meaningful supporting scientific evidence, include hyssop, ivy leaf, linden, marshmallow, mistletoe, mullein, oregano, and peppermint.

In a double-blind, placebo-controlled trial, colostrum was not helpful for people with sore throat.142 (The researchers made sure to exclude people with strep throat, but some participants may have had sore throat caused by bacteria rather than cold viruses.)

A substantial (254-participant), double-blind, placebo-controlled study failed to find that use of the berry of Hippophae rhamnoides (sea buckthorn) reduced the number or duration of colds.161

A 2009 review of 17 trials found that there is limited evidence to support the use of Traditional Chinese herbal preparations for the common cold.171

A randomized trial involving 410 people with H1N1 influenza found that those who took a combination of 12 Chinese herbal medicines (maxingshigan-yinqiaosan, 200 mL, 4 times daily) along with the antiviral medication oseltamivir (75 mg twice daily) for five days experienced a more rapid resolution of fever compared to those taking oseltamivir alone.176

Homeopathic approaches to colds and flus are also discussed in the Homeopathy database, in two separate chapters titled, respectively, influenza and common cold.