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NCCIH Clinical Digest

for health professionals

Travel-Related Ailments and Complementary Health Approaches: What the Science Says

June 2022

Clinical Guidelines, Scientific Literature, Info for Patients: 
Travel-Related Ailments and Complementary Health Approaches

travel related illness

Malaria Prophylaxis and Treatment

Many consumer websites promote “natural” ways to prevent or treat malaria, which often involve dietary changes or herbal products, such as quinine from the cinchona tree (Cinchona spp.) or extracts and material from the artemisia plant (Artemisia annua L. or sweet wormword).

Travelers should follow official recommendations and not rely on unproven “natural” approaches in an attempt to prevent or treat such a serious disease. 

Travelers’ Diarrhea

It has been claimed that a variety of products, including probiotics, goldenseal, activated charcoal, and grapefruit seed extract, can prevent or treat travelers’ diarrhea (TD).


Although some studies on probiotics for the prevention of TD had promising results, meta-analyses have reached conflicting conclusions. It is difficult to interpret the evidence because studies have used a variety of microbial strains, some studies were not well controlled, and the optimal dose and duration of use have not been defined. 


No high-quality research on goldenseal for TD has been published. 

Activated Charcoal

There is no evidence to support the 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. 

Grapefruit Seed Extract

Claims that grapefruit seed extract can prevent bacterial foodborne illnesses are not supported by research. 


  • In healthy people, probiotics usually have only minor side effects, if any.
  • Studies show that goldenseal inhibits cytochrome P450 enzymes, raising concerns that it may increase the toxicity or alter the effects of drugs.
  • Children should not be given activated charcoal for diarrhea or dehydration. It may absorb nutrients, enzymes, and antibiotics in the intestine and mask the severity of fluid loss.
  • People who need to avoid grapefruit because it interacts with medicine that they are taking should also avoid grapefruit seed extract.

Altitude Illness

There is little, if any, evidence that dietary or herbal supplements help prevent or treat altitude illness.


Coca leaf (chewed or made into tea) has been used for altitude illness, but there is no strong evidence on whether it works or has adverse effects. It will result in a positive drug test for cocaine metabolites.


There is no evidence supporting claims that garlic helps reduce altitude illness. 

Ginkgo biloba

Studies of ginkgo for preventing altitude illness are inadequate to justify recommendations about its use. 

Vitamin E

Only one small study has investigated vitamin E, in combination with other antioxidants, for altitude illness, and no significant benefit was observed.


  • Garlic supplements appear safe for most adults. Possible side effects of taking garlic 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 of drug interactions.
  • Products made from standardized ginkgo leaf extracts appear to be safe when used as directed. However, ginkgo may increase the risk of bleeding in some people and interact with anticoagulants. In addition, studies by the National Toxicology Program showed that rodents developed tumors after being given a ginkgo extract for up to 2 years.

Motion Sickness

Complementary approaches marketed for preventing or treating motion sickness include acupressure, magnets, ginger, pyridoxine, and homeopathic remedies.

Acupressure and Magnets

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


Although some studies have shown that ginger may ease pregnancy-related nausea and vomiting, there is no strong evidence that it helps with motion sickness.

Homeopathic Products

There is no evidence supporting claims that homeopathic products prevent or alleviate motions sickness. 

Pyridoxine (Vitamin B6)

Although an American College of Obstetricians and Gynecologists 2015 Practice Bulletin Summary recommends pyridoxine alone or in combination with doxylamine (an antihistamine) as a safe and effective treatment for nausea and vomiting associated with pregnancy, there is no evidence supporting claims that pyridoxine prevents or alleviates motion sickness.


  • In some people, ginger can have mild side effects such as abdominal discomfort. Research has not definitely shown whether ginger interacts with medications, but concerns have been raised that it might interact with anticoagulants. The effect of using ginger supplements with common over-the-counter drugs for motion sickness is unknown.
  • Taking excessive doses of pyridoxine supplements for long periods of time can affect nerve function.

Jet Lag/Sleep Problems

Complementary approaches that have been suggested for jet lag or other sleep problems include the dietary supplement melatonin; relaxation techniques and other mind and body practices; aromatherapy; and herbs such as chamomile, kava, and valerian.


Some evidence suggests that melatonin supplements may help with sleep problems caused by jet lag in people traveling either east or west.

Relaxation Techniques

Relaxation techniques, such as progressive relaxation, and other mind and body practices, such as mindfulness-based stress reduction, may help with insomnia, but it has not been established if they are effective for jet lag.

Aromatherapy and Herbs

There is very little evidence that aromatherapy or the herbs chamomile or valerian help with insomnia.

Another herb, kava, is also promoted for sleep but good research on its effectiveness is lacking.


  • Melatonin is sold as a dietary supplement; dietary supplements are regulated less strictly than drugs. The amounts of ingredients in dietary supplements may 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 there was substantial lot-to-lot variation. Also, 26% of products contained serotonin as a contaminant. 
  • Melatonin supplements appear to be safe for most people when used short-term; less is known about their long-term safety. The absence of long-term studies, however, makes it challenging to know with certainty the safety and tolerability of melatonin with continued use. 
  • 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%), headache (0.74%), other sleep-related adverse events (0.74%), dizziness (0.74%), and hypothermia (0.62%). Almost all adverse events were considered mild or moderate in severity and tended to resolve either spontaneously or after discontinuing treatment. 
  • People with epilepsy or who take an oral anticoagulant should never use melatonin without medical supervision. 
  • Travelers should not take melatonin early in the day because it can cause sleepiness and delay adaptation to local time.
  • Relaxation techniques are safe for most people.
  • Significant side effects from aromatherapy and herbs are uncommon, but chamomile can cause allergic reactions and kava supplements have been linked to a risk of severe liver damage.

Insect Protection

Many products are promoted as “natural” insect repellents, and their use may appeal to people who prefer not to use synthetic products. Products promoted as natural mosquito repellents include citronella products, oil of lemon eucalyptus (OLE), and neem oil (a component of agricultural insecticide products that is promoted on some websites for home use). Essential oils and other natural products are promoted to repel bed bugs.


Laboratory studies found that botanicals, including citronella products, worked for shorter periods than products containing DEET. For people who prefer to use botanicals, the Centers for Disease Control and Prevention (CDC) recommends Environmental Protection Agency (EPA)-registered products containing OLE.

The evidence does not support the use of neem oil as a natural repellent. 

Bed Bugs

There is no evidence that the natural products marketed to repel bed bugs are effective. Instead, travelers should be encouraged to follow steps to detect and avoid bed bugs, such as inspecting their mattresses and keeping their luggage off the floor or bed.


  • The FDA has recommended that OLE or p-menthane-3, 8-diol (PMD) not be used in children under 3 years of age.

Sun Protection

Many “natural” sunscreen products are promoted online, as are recipes for making your own along with advice on consuming dietary supplements or drinking teas to protect against sun damage.

Studies have not proven that any herbal product or dietary supplement, including aloe vera, beta carotene, selenium, or epigallocatechin gallate (EGCG), an extract from green tea, reduces the risk of skin cancer or sun damage. 


  • Experts recommend using a broad-spectrum sunscreen, limiting your sun exposure, and wearing protective clothing to protect against sunburns and to possibly lower the risk of skin cancer.

Homeopathic Vaccines

There is no credible scientific evidence or plausible scientific rationale to support claims that products called “nosodes” or homeopathic vaccines are effective substitutes for conventional immunizations.

Colds and 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 flu include zinc products; neti pots and other forms of saline nasal irrigation; vitamin C; probiotics; echinacea; and other herbs.


Taking zinc orally (often in the form of lozenges) may reduce the duration of a cold.

Nasal Irrigation and Neti Pots

Nasal saline irrigation, such as with neti pots, may be useful and safe for chronic sinusitis. It may also help relieve the symptoms of acute upper respiratory tract infections, but the evidence is not definitive.

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 may lead to shorter colds but taking it only after cold symptoms appear does not. 


The quality of the evidence is very low that probiotics might reduce susceptibility to colds or other upper respiratory tract infections and the duration of the illnesses. 


A 2014 systematic review concluded that echinacea has not been convincingly shown to be effective; however, a weak effect has not been ruled out.

There is no strong evidence 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.


  • Zinc, particularly in large doses, can have side effects including nausea and diarrhea. The intranasal use of zinc can cause anosmia (loss of sense of smell), which may be long-lasting or permanent.
  • 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.
  • Vitamin C supplements appear safe, even at high doses.


  • Shurtleff D, Meister K, Stout S. Discussing complementary and integrative health approaches with travelers. In: Brunette GW, Kozarsky PE, Brown CM, et al., eds. CDC Yellow Book 2022: Health Information for International Travel. New York, NY: Oxford University Press. [in press]

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

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