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National Center for Complementary and Integrative Health

NCCIH Clinical Digest

for health professionals

Spotlight on Herbs and Other Botanicals: What the Science Says

November 2024

Clinical Guidelines, Scientific Literature, Info for Patients: 
Spotlight on Herbs and Other Botanicals

images of herbs

Cranberry

Cranberry has a history of traditional use in dyes, food, and medicine among Native Americans and later European settlers. Cranberry products may decrease the overall risk of recurrent urinary tract infections (UTIs) in women who have had previous UTIs; however, it isn’t recommended as a treatment for existing UTIs. The U.S. Food and Drug Administration allows claims about this potential benefit to appear on labels of cranberry dietary supplements and cranberry juice beverages.   

What Does the Research Show?

  • In general, cranberry products may decrease the overall risk of symptomatic, recurrent UTIs in women by 25 percent, and in some cases, by more than 30 percent, according to a 2023 Cochrane review. However, the effectiveness of cranberry is still in question because of inconsistent findings.
  • While cranberry may assist in preventing symptomatic UTIs in some women, it isn’t recommended as a treatment for existing UTIs in any population.
  • According to the American Urological Association, the mechanisms of action are thought to be related to the proanthocyanidins (PACs) present in cranberries that prevent bacteria from sticking to the bladder wall, thus preventing the start of a UTI. Processing cranberries into various products, like tablets or capsules, can reduce the concentration of PACs, which can reduce the potential effectiveness of a product.
  • Studies in certain populations at increased risk for UTIs, such as elderly people in long-term care and pregnant women, have had inconsistent results. Studies in other high-risk populations, such as women undergoing gynecological surgeries or people with multiple sclerosis, have not found cranberry to be beneficial in reducing the risk for UTIs.
  • Starting in 2020, the U.S. Food and Drug Administration has allowed manufacturers to claim on product labels that there is “limited” evidence that daily consumption of specified amounts of cranberry dietary supplements may reduce the risk of recurrent UTIs in healthy women. A similar claim may be made for cranberry juice beverages, but the evidence must be described as “limited and inconsistent.”

Safety

  • Cranberry taken orally is generally thought to be safe. However, if consumed in very large amounts, cranberry can cause stomach upset and diarrhea, particularly in young children.
  • There is conflicting evidence about whether cranberry interacts with the anticoagulant warfarin. 
  • Some studies of the use of cranberry during pregnancy or while breastfeeding suggest it is safe in amounts commonly found in food, but the evidence is not conclusive for use in larger amounts. 

Cinnamon

Cinnamon has a long history of use in traditional medicine and cuisine in many parts of the world. Currently, cinnamon is promoted for a variety of health conditions, particularly diabetes and weight loss. However, the results of the research on cinnamon are hard to interpret because it’s often unclear which species or part of the cinnamon plant was tested. 

What Does the Research Show?

  • Research doesn’t clearly support using cinnamon for any health condition.
  • It’s unclear whether cinnamon supplementation is helpful for diabetes or weight loss. Higher quality research would be needed to clarify any benefits.
  • Preliminary research indicates that a nasal spray containing Ceylon cinnamon extract might improve symptoms of allergic rhinitis, but more reliable evidence is needed to confirm this initial result.
  • It’s unclear whether cassia cinnamon is effective as a mosquito repellant.

Safety

  • Cinnamon is likely safe when consumed in the amounts commonly used in foods as a spice or flavoring agent. When used in larger amounts or for long periods of time, cinnamon is sometimes associated with side effects, most commonly gastrointestinal problems or allergic reactions.
  • Cinnamon products may not clearly indicate which species (e.g., Ceylon, cassia) or parts (e.g., bark, leaves, roots) of cinnamon have been used in the making of a product. Research indicates that the types and parts of cinnamon have important differences in chemical composition, and these differences can affect the product’s impact on people.
  • Interactions between coumarin, a chemical found in cassia cinnamon, and the liver have been reported. Consuming cassia cinnamon doesn’t usually include enough coumarin to cause significant problems; however, some cassia cinnamon products contain high levels of coumarin. Prolonged use of cassia cinnamon could be an issue for sensitive people, such as those with liver disease. Ceylon cinnamon may contain a trace amount of coumarin.
  • Some types of topical cinnamon oil or powder may cause skin irritation or contact dermatitis, according to reports.
  • According to research partially funded by the National Center for Complementary and Integrative Health, there are theoretical reasons to suspect that some components of cinnamon may interact with an anticancer medicine or nicotine. 
  • Some studies of the use of Ceylon and cassia cinnamon during pregnancy suggest it is safe in amounts commonly found in foods, but Ceylon cinnamon in larger amounts during pregnancy is considered unsafe. Little is known about whether it’s safe to use Ceylon or cassia cinnamon in larger amounts while breastfeeding.

Sage

Sage has a long history of use as a spice and for health purposes. There have been a few studies of this herb for sore throat, mood, memory, diabetes, and blood cholesterol levels, but the findings are preliminary, and some of the research is of poor quality. Sage has not been clearly shown to be helpful for any health condition. 

What Does the Research Show?

  • Little is known about the health effects of sage because research is scant. Sage has not been clearly shown to be helpful for any health condition.
  • There have been a few studies of sage for sore throat, mood, memory, diabetes, and blood cholesterol levels. However, the findings are preliminary, and some of the research is of poor quality.

Safety

  • Sage is safe in the amounts commonly found in foods, and larger amounts have been used safely for up to 4 months in research studies. However, some species of sage, including common sage (Salvia officinalis), contain a constituent called thujone that has caused seizures in animal models. Cases of seizures associated with consumption of sage essential oil (which is high in thujone) have been reported in people. High-dose or long-term use of sage may not be safe.
  • It may be unsafe to use sage during pregnancy because its constituent thujone may have harmful effects. Little is known about whether it’s safe to use sage while breastfeeding.

Elderberry

Elderberry (also called European elder) has been used in folk medicine to treat colds and flu. Some preliminary research suggests that elderberry may relieve symptoms of flu, colds, or other upper respiratory infections.

What Does the Research Show?

  • Some preliminary research suggests that elderberry may relieve symptoms of flu, colds, or other upper respiratory infections. 
  • The U.S. Food and Drug Administration and Federal Trade Commission have taken action against companies that marketed products with unsubstantiated claims of effectiveness for COVID-19. 
  • There’s not enough information to show whether elderberry is helpful for any other health purposes.

Safety

  • Raw or unripe elderberries and other parts of the elder tree, such as the leaves and stem, contain poisonous cyanide-producing substances that can cause nausea, vomiting, and severe diarrhea; cooking eliminates this toxin. Large quantities of the toxin may cause serious illness.     
  • Little is known about whether it’s safe to use elderberry for health purposes during pregnancy or while breastfeeding.

European Mistletoe

European mistletoe has been used for centuries in traditional medicine for a variety of conditions, including seizures, headaches, and menopause symptoms. There have been clinical trials of European mistletoe for cancer treatment, mostly in Europe. Although some trials indicated that European mistletoe improved survival or quality of life, many of the trials had major weaknesses that raise doubts about their findings. European mistletoe is not a proven cancer treatment and should not be used as a treatment for cancer outside of clinical trials.

What Does the Research Show?

  • There have been clinical trials of European mistletoe for cancer treatment, mostly in Europe. Although some trials indicated that European mistletoe improved survival or quality of life, many of the trials had major weaknesses that raise doubts about their findings. These weaknesses have included small sample size, lack of information about the dosage, and methodological problems. 
  • A preliminary trial conducted by the National Center for Complementary and Integrative Health and the National Cancer Institute evaluated the safety of injected European mistletoe extract in combination with a cancer drug in patients with advanced cancer and found that patients could tolerate the herb/drug combination.

Safety

  • European mistletoe berries and leaves can cause serious harmful effects when taken orally. 
  • Injected European mistletoe extract may cause soreness and inflammation at the injection site, headache, fever, and chills. A few severe allergic reactions have been reported. 
  • European mistletoe is probably unsafe for use during pregnancy. Little is known about whether it’s safe for use while breastfeeding.

References

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.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH’s Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH website at nccih.nih.gov. NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.

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