Author(s): David Shurtleff, Kathleen Meister, Shawn Stout

Travelers often ask their health care providers about the use of complementary or integrative health approaches for travel-related illnesses and conditions. Claims made about dietary supplements, herbal products (see Box 2-15), and other complementary approaches for travel-related health problems may not be supported by evidence. Be prepared to discuss what is known about the reported benefits of complementary and integrative health approaches and to counsel travelers on their possible side effects or interactions with prescribed vaccines or medications.

Claims Versus Science

Altitude Illness

Many natural products, including coca leaf, garlic, Ginkgo biloba, and vitamin E, have been promoted for preventing or treating altitude illness. For more information on altitude illness, see Sec. 4, Ch. 5, High Elevation Travel & Altitude Illness.

Coca Leaf

Coca leaf, chewed or made into tea, has been used for altitude illness, but no strong evidence has shown that it works or that it has adverse effects. Travelers should be aware that using coca leaf will cause a positive drug test result for cocaine metabolites.

Garlic

No evidence supports claims that garlic helps reduce altitude illness. Garlic supplements appear safe for most adults. Possible side effects include breath and body odor, heartburn, and upset stomach. Some people have allergic reactions to garlic. Short-term use of most commercially available garlic supplements poses only a limited risk for drug interactions.

Ginkgo Biloba

Studies of Ginkgo biloba for preventing altitude illness are inadequate to justify recommendations about its use. Products made from standardized ginkgo leaf extracts appear to be safe when used as directed. However, ginkgo can increase the risk of bleeding in some people and interact with anticoagulants. In addition, studies by the National Toxicology Program showed that rodents developed liver and thyroid tumors after being given a ginkgo extract for up to 2 years.

Vitamin E

One study investigated vitamin E, in combination with other antioxidants, for altitude illness; no significant benefit was observed.

Colds & Flu

Although colds and flu are not uniquely travel-related hazards, many people try to avoid these illnesses during a trip. Complementary health approaches that have been advocated for preventing or treating colds or influenza include echinacea, garlic and other herbs, nasal saline irrigation, probiotics, vitamin C, zinc products, and others.

Echinacea

Numerous studies have tested the herb echinacea to see whether it can prevent colds or relieve cold symptoms. A 2014 systematic review concluded that echinacea has not been convincingly shown to be effective; however, a weak effect was not ruled out.

Garlic & Other Herbs

No strong evidence supports claims that garlic, Chinese herbs, oil of oregano, or eucalyptus essential oil prevent or treat colds, or that the homeopathic product Oscillococcinum prevents or treats influenza or influenza-like illness.

Nasal Saline Irrigation

Nasal saline irrigation (e.g., use of neti pots), can be useful and safe for chronic sinusitis. Nasal saline irrigation also can help relieve the symptoms of acute upper respiratory tract infections, but the evidence is not definitive. Even in places where tap water is safe to drink, people should use only sterile, distilled, boiled-then-cooled, or specially filtered water for nasal irrigation to avoid the risk of introducing waterborne pathogens.

Probiotics

Probiotics might reduce susceptibility to colds or other upper respiratory tract infections and the duration of the illnesses, but the quality of the evidence is low or very low.

Vitamin C

Taking vitamin C supplements regularly reduces the risk of catching a cold among people who perform intense physical exercise, but not in the general population. Taking vitamin C on a regular basis might lead to shorter-duration colds, but taking it only after cold symptoms appear does not. Vitamin C supplements appear to be safe, even at high doses.

Zinc

Zinc taken orally, often in the form of lozenges, within 24 hours of symptom onset might reduce the duration of a cold. No firm recommendation currently can be made, however, regarding prophylactic zinc supplementation because of insufficient data. When taken in large doses, side effects from zinc can include nausea and diarrhea, copper deficiency, and decreased absorption of some medications. Intranasal use of zinc can cause anosmia (loss of sense of smell), which can be long-lasting or permanent.

Coronavirus Disease 2019

A variety of dietary supplements, including elderberry, melatonin, colloidal silver, vitamin C, vitamin D, and zinc have each been suggested to prevent or treat coronavirus disease 2019 (COVID-19). Except for colloidal silver (for which no plausible mechanism of action exists), the listed supplements have theoretical applications in preventing or treating COVID-19; evidence of efficacy from clinical trials is limited, however, and without clear demonstration of benefit. In addition, use of colloidal silver and zinc carries health and safety concerns. Colloidal silver (and other silver products) can cause argyria, a permanent blue-gray discoloration of the skin and other organs. High-dose supplementation with zinc can cause nausea and diarrhea, copper deficiency, and decreased absorption of some medications. The National Institutes of Health (NIH) COVID-19 Treatment Guidelines recommend against supplementation with zinc above the recommended dietary allowance because of these risks and the lack of evidence of clinical benefit.

The NIH COVID-19 Treatment Guidelines provide up-to-date guidance on dietary supplements and COVID-19 for health care providers and travelers. For additional information on COVID-19 prevention and treatment, see Sec. 5, Part 2, Ch. 3, COVID-19.

Homeopathic Vaccines

Proponents of homeopathy claim that products called nosodes, or homeopathic vaccines, are effective substitutes for conventional immunizations. No credible scientific evidence or plausible scientific rationale supports these claims. For more information on travel vaccines, see Sec. 2, Ch. 3, Vaccination & Immunoprophylaxis—General Principles.

Insect Repellents

Many products are promoted as “natural” insect repellents, and their use can appeal to people who prefer not to use synthetic products. Products promoted as natural mosquito repellents include citronella products, neem oil (a component of agricultural insecticide products promoted on some websites for home use), and oil of lemon eucalyptus (OLE). Essential oils and other natural products are promoted to repel bed bugs. Travelers should use only Environmental Protection Agency (EPA)–registered insect repellents; more information is available at the EPA website.

Botanicals

Laboratory-based studies found that botanicals, including citronella products, worked for shorter periods than products containing DEET (N,N-diethyl-m-toluamide or N,N-diethyl-3-methyl-benzamide). For people who choose to use botanicals, the Centers for Disease Control and Prevention (CDC) recommends EPA-registered products containing OLE (oil of lemon eucalyptus). Limited evidence suggests that neem oil could be beneficial as a natural repellent. For more information on insect repellents, see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods).

Bed Bug Repellents

No evidence supports effectiveness of natural products marketed to repel bed bugs. Instead, encourage travelers to follow steps to detect and avoid bed bugs (e.g., inspecting mattresses, keeping their luggage off the floor or bed). More information is available at CDC’s Parasites website and in Section 4, Box 4-10, Recommended protective measures to avoid or reduce bed bug exposure.

Jet Lag & Sleep Problems

Complementary approaches suggested for jet lag or other sleep problems include aromatherapy and herbs (e.g., chamomile, kava, valerian); the dietary supplement melatonin; and relaxation techniques. See Sec. 8, Ch. 4, Jet Lag, for more information.

Aromatherapy

Very little evidence supports the belief that aromatherapy or the herbs chamomile or valerian help with insomnia. Major side effects are uncommon, but chamomile can cause allergic reactions. Another herb, kava, also is promoted for sleep, but good research on its effectiveness is lacking. More importantly, kava supplements have been linked to a risk of severe liver damage.

Melatonin

Some evidence suggests that melatonin supplements can help with sleep problems caused by jet lag in people traveling either east or west. Melatonin is sold as a dietary supplement; dietary supplements are less strictly regulated than drugs. The amounts of ingredients in dietary supplements can vary, and product contamination is a potential concern. A 2017 analysis of melatonin supplements sold in Canada found that their actual melatonin content ranged from <83% to >478% of the labeled content and that substantial lot-to-lot variation was evident. Also, 26% of products contained serotonin as a contaminant. Melatonin supplements appear to be safe for most people who use them for discrete periods of time; an absence of studies examining the effects associated with continued use makes it challenging to know with certainty its long-term safety and tolerability. In a 2019 systematic review of mostly short-term trials of melatonin for sleep problems, the most frequently reported adverse events were daytime sleepiness (1.66%), dizziness (0.74%), headache (0.74%), other sleep-related adverse events (0.74%), and hypothermia (0.62%). Almost all adverse events were considered mild–moderate in severity and tended to resolve either spontaneously or after discontinuing treatment.

Caution people with epilepsy or who take an oral anticoagulant against using melatonin without medical supervision. In addition, advise travelers not to take melatonin early in the day, because it can cause sleepiness and delay adaptation to local time.

Relaxation Techniques

Relaxation techniques (e.g., progressive relaxation and other mind and body practices, including mindfulness-based stress reduction) can help with insomnia, but their effectiveness for jet lag has not been established.

Malaria

Many consumer websites promote “natural” ways to prevent or treat malaria, which often involve dietary changes or herbal products (e.g., quinine from the cinchona tree [Cinchona spp.]) or extracts and material from the artemisia plant (Artemisia annua L. or sweet wormwood). Strongly urge patients to follow official recommendations, including the use of malaria chemoprophylaxis, and not to rely on unproven “natural” approaches to prevent or treat such a serious disease. Recommended drugs to prevent and treat malaria are described in Sec. 5, Part 3, Ch. 16, Malaria.

Motion Sickness

Complementary approaches advocated for preventing or treating motion sickness include acupressure and magnets, ginger, homeopathic remedies, and pyridoxine (vitamin B6).

Acupressure & Magnets

Research does not support the use of acupressure or magnets for motion sickness.

Ginger

Although some studies have shown that ginger might ease pregnancy-related nausea and vomiting, no strong evidence shows that it helps with motion sickness. In some people, ginger can have mild side effects (e.g., abdominal discomfort). Research has not definitively shown whether ginger interacts with medications, but concerns have been raised that it could interact with anticoagulants. The effect of using ginger supplements with common over-the-counter drugs for motion sickness (e.g., dimenhydrinate [Dramamine]) is unknown.

Homeopathic Remedies

No evidence supports claims that homeopathic products prevent or alleviate motion sickness.

Pyridoxine (Vitamin B6)

Although an American Congress of Obstetrics and Gynecology 2015 Practice Bulletin Summary recommends pyridoxine (vitamin B6) alone or in combination with doxylamine (an antihistamine) as a safe and effective treatment for nausea and vomiting associated with pregnancy, no evidence supports claims that pyridoxine prevents or alleviates motion sickness. Taking excessive doses of pyridoxine supplements for long periods of time can affect nerve function.

Sun Protection

Many “natural sunscreen” products are promoted online, as are recipes for homemade sunscreen and advice on consuming dietary supplements or drinking teas to protect against sun damage. No studies have proven that any dietary supplement or herbal product, including aloe vera, beta carotene, epigallocatechin gallate (EGCG; a green tea extract), or selenium reduces the risk for skin cancer or sun damage. For more information, see Sec. 4, Ch. 1, Sun Exposure.

Travelers’ Diarrhea

A variety of products, including activated charcoal, goldenseal, grapefruit seed extract, and probiotics are claimed to prevent or treat travelers’ diarrhea (TD). Counsel travelers about food and water safety precautions. For more information, see Sec. 2, Ch. 8, Food & Water Precautions.

Activated Charcoal

No solid evidence supports claims that activated charcoal helps with TD, bloating, stomach cramps, or gas. The side effects of activated charcoal have not been well documented but were mild when it was tested on healthy people. Children should not be given activated charcoal for diarrhea and dehydration because it can absorb nutrients, enzymes, and antibiotics in the intestine and mask the severity of fluid loss.

Goldenseal

No high-quality research has been published on goldenseal for TD. Studies show that goldenseal inhibits cytochrome P450 enzymes, raising concerns that goldenseal might increase the toxicity or alter the effects of some drugs.

Grapefruit Seed Extract

Claims that grapefruit seed extract can prevent bacterial foodborne illnesses are not supported by research. People who need to avoid grapefruit because it interacts with medicine they are taking should also avoid grapefruit seed extract.

Probiotics

To date, insufficient evidence exists to draw definite conclusions about the efficacy of probiotics for the prevention of TD. Although some studies have had promising results, meta-analyses have reached conflicting conclusions. Interpretation of the evidence is difficult because studies have used a variety of microbial strains, some studies were not well controlled, and the optimal doses and duration of use have not been defined. For more information, see Sec. 2, Ch. 6, Travelers’ Diarrhea.

Untested Therapies Used In Other Countries

CDC does not recommend traveling to other countries for untested medical interventions or to buy medications that are not approved in the United States. For more information see the chapters in Section 6, Health Care Abroad.

Talking To Travelers About Complementary Health Approaches

Given the vast number of complementary or integrative interventions and the wealth of potentially misleading information about them that can be found on the internet, discussing the use of these approaches with patients can seem daunting. Be proactive, though, because surveys show that many patients are reluctant to raise the topic with health care providers. Federal agencies (e.g., the National Center for Complementary and Integrative Health [NCCIH]) offer evidence-based resources to help providers and their patients have meaningful discussions about complementary approaches.

Acknowledgments

The authors thank Mr. Philip Kibak of ICF for his editorial assistance.