Herb |
What Science Says |
Side Effects and Cautions |
Cranberry |
Some evidence that it may help prevent urinary tract infections; has not been found to effectively treat urinary tract infections
May help impair the ability of Helicobacter pylori to live in the stomach
May help reduce dental plaque |
Appears safe; excessive intake could cause gastrointestinal (GI) upset or diarrhea
Some indications that it should be used cautiously by people on anticoagulants, medications that affect the liver, and aspirin |
Garlic |
Some evidence suggests it may slightly reduce serum cholesterol levels and also slow the development of atherosclerosis.
May lower blood pressure, especially in people with hypertension
No clinical trials have examined the effect of garlic on lowering cancer risk. |
Safe for most adults
Side effects include breath and body odor, heartburn, GI upset, and allergic reactions; side effects are more common with raw garlic
May increase prothrombin time and enhance the effects and adverse effects of anticoagulant and antiplatelet medications
Interferes with the effectiveness of saquinavir, a drug to treat HIV |
Saw palmetto |
Has not been found to reduce urinary symptoms associated with benign prostatic hypertrophy or any other conditions |
Well tolerated; may cause stomach discomfort in some |
Soy |
Daily intake may slightly lower low-density lipoprotein (LDL) cholesterol.
May reduce hot flashes in postmenopausal women but study results are inconsistent
Not enough evidence to determine if it is effective for any other health issues |
Is considered safe for most people when used as a food or taken for short periods of time as a supplement
The safety of long-term use of soy isoflavones has not been established.
Its role in breast cancer risk is uncertain. |
Ginkgo biloba |
Not effective in lowering the overall incidence of dementia and Alzheimer disease in the elderly
Has not shown significant benefit for intermittent claudication
Conflicting evidence that it helps tinnitus |
Side effects may include headache, nausea, GI upset, diarrhea, dizziness, or allergic skin reactions.
May increase bleeding risk
Rats and mice given a specific ginkgo extract for up to 2 years developed tumors; research is needed to determine whether ginkgo affects cancer risk in people. |
Milk thistle |
Small clinical trials evaluating its efficacy in protecting and promoting the growth of liver cells, fighting oxidation, and inhibiting inflammation have been mixed and two rigorously designed studies found no benefit. |
Well tolerated
May cause allergic reaction in people allergic to plants in the daisy family (ragweed, chrysanthemums, marigolds, daisies)
May lower blood glucose levels; should be used with caution by people with diabetes or hypoglycemia |
Black cohosh |
Results are mixed on whether it effectively relieves menopausal symptoms. A National Center for Complementary and Integrative Health (NCCIH)-funded study found it did not relieve hot flashes and night sweats in perimenopausal or postmenopausal women when used alone or in combination with other herbs. |
Experts suggest women should stop using black cohosh and consult a health-care provider if they have a liver disorder or develop symptoms of impaired liver function. Although there are reports of hepatitis and liver failure in women using black cohosh, it is not certain that black cohosh is to blame.
In general, studies evaluating it for menopausal symptoms have not found serious side effects.
It is not known whether it is safe for women who have had hormone-sensitive conditions, such as breast cancer. |
Echinacea |
Results of studies on whether it can prevent or treat upper respiratory tract infections are mixed. |
Mostly well tolerated; GI side effects are most common.
May cause allergic reaction in people allergic to plants in the daisy family (ragweed, chrysanthemums, marigolds, daisies) and those with asthma or a genetic tendency toward allergic reactions |
St. John’s wort |
Has not been found to be more effective than placebo in treating minor depression or major depression of moderate severity |
Interacts with numerous medications, including antidepressants, birth control pills, cyclosporine, digoxin, indinavir, antiseizure medications, and warfarin and related anticoagulants
May cause increased sensitivity to sunlight; may also cause anxiety, dry mouth, dizziness, GI symptoms, fatigue, headache, or sexual dysfunction |
Ginseng |
Some studies show it may lower blood glucose; other studies suggest possible beneficial effects on immune function.
Research results do not conclusively support health claims associated with ginseng. |
Likely safe when taken by mouth for a short period of time
May cause headaches, sleep problems, and GI problems diarrhea
Asian ginseng can cause allergic reactions. |
*Lindstrom, A., Ooyen, C., Lynch, M. E., & Blumenthal, M. (2013). Herb supplement sales increase 5.5% in 2012: Herbal supplement sales rise for 9th consecutive year; turmeric sales jump 40% in natural channel. HerbalGram, 99, 60-65. Available at http://cms.herbalgram.org/herbalgram/issue99/hg99-mktrpt.html. Accessed on 3/25/16.
†National Center for Complementary and Integrative Health, National Institutes of Health. Herbs at a glance. Available at https://nccih.nih.gov/health/herbsataglance.htm. Accessed on 3/25/16. |