Photo of popular botanicals green tea, black cohosh, cranberry, ginger, and beetroot, clockwise from top.
Clockwise from top: green tea, black cohosh, cranberry, ginger, beetroot.

All supplement ingredients below are derived from plants. But they vary in efficacy and safety. See a partial list of supplement ingredients to outright avoid.

Note: Information on use, efficacy, and safety is primarily based on research compiled by the National Institutes of Health’s National Center for Complementary and Integrative Health and Office of Dietary Supplements.

Beetroot

Reasons for Use
Generally sold as a powder that can be mixed into a juice, to improve athletic performance.

How Well It Works
Though research has yielded conflicting results, studies suggest it might improve performance in endurance sports, such as running, swimming, rowing, and cycling.

Known Risks
More research is needed, but there have not been major safety concerns identified with moderate consumption (2 cups a day) for several weeks, as is commonly recommended.

Black Cohosh

Reasons for Use
To treat menopausal symptoms and sometimes menstrual cramps, or to induce labor.

How Well It Works
Knowledge is limited, with insufficient evidence to support use.

Known Risks
While black cohosh itself has been shown to be generally safe when taken for as long as a year, many black cohosh products have been found to contain unlisted herbs mixed in. Cases of liver damage have also been linked to black cohosh, potentially because of the other herbs.

Chamomile

Reasons for Use
For sleeplessness, anxiety, and gastrointestinal conditions.

How Well It Works
It’s not well-studied, though preliminary research indicates that it may be helpful for anxiety and may ease an upset stomach if taken in combination with other herbs, including milk thistle and peppermint.

Known Risks
As a tea, it’s generally considered safe. Some people allergic to plants such as ragweed may have a reaction to chamomile. It can also interact with drugs used after organ transplants, as well as with some blood thinners.

Cranberry

Reasons for Use
Mostly used to treat urinary tract infections (UTIs).

How Well It Works
Evidence is mixed. Some studies indicate that cranberry may reduce UTI risk for certain people, but research hasn’t shown that it works as a UTI treatment.

Known Risks
Drinking cranberry juice is generally safe, though it’s usually high in sugar. Large quantities can lead to upset stomach, and drinking a lot of cranberry juice on a regular basis can increase the risk of kidney stones. Cranberry supplements may interact with blood-thinning drugs.

Ginger

Reasons for Use
Commonly used to treat nausea and vomiting and sometimes for other conditions, including arthritis and motion sickness.

How Well It Works
Ginger may help with nausea related to pregnancy and chemotherapy, studies have shown. Evidence is less certain on whether it can ease other types of nausea or conditions.

Known Risks
Usually considered safe when used as a spice. Some users may experience gas and heartburn; it may also be problematic for people with gallstones. And it can interact with blood-thinning meds.

Green Tea Extract

Reasons for Use
Mainly to improve alertness, relieve digestive symptoms, and promote weight loss.

How Well It Works
Green tea seems to make people more alert, probably because of the caffeine. There’s not good evidence that it helps people lose weight.

Known Risks
Drinking green tea in moderate amounts is believed to be safe. But green tea extract has been linked to serious problems, including liver damage, elevated blood pressure, increased heart rate, and even death. CR recommends avoiding green tea extract supplements.

Milk Thistle

Reasons for Use
Mostly used for liver problems related to conditions such as hepatitis and cirrhosis.

How Well It Works
Results have been uneven. Some research shows that certain patients who take milk thistle have milder symptoms from liver disease; other studies have found that it’s no better than a placebo.

Known Risks
Well-tolerated in recommended doses, though some report gastrointestinal problems. Can trigger allergic reactions, especially for people also allergic to ragweed. Diabetics should also use caution with milk thistle because it may lower blood sugar levels.

Saw Palmetto

Reasons for Use
To treat the symptoms of an enlarged prostate—an age-related condition in men that can make urination difficult.

How Well It Works
Small studies suggested a possible benefit, but the best well-designed large studies have concluded that it’s no more effective than a placebo.

Known Risks
There are few known side effects, though some people experience mild ones, such as headaches.

St. John’s Wort

Reasons for Use
Primarily for depression; sometimes to treat menopause symptoms, attention deficit hyperactivity disorder, and obsessive-compulsive disorder.

How Well It Works
It seemed to ease depression in a few studies, but results are mixed. Evidence indicates it is not helpful for ADHD or other conditions.

Known Risks
It can interact in life-threatening ways with certain drugs and has been shown to weaken antidepressants, birth control pills, some cancer drugs, and warfarin. It has also been linked to side effects such as anxiety, fatigue, and sexual dysfunction.

Valerian

Reasons for Use
Mainly used to treat insomnia, though some also use it to treat anxiety, depression, or menopause symptoms.

How Well It Works
It’s unclear how much valerian helps with sleep because there’s not much rigorous research on the topic and results of existing studies have varied. There’s too little evidence to know whether it can help with other conditions.

Known Risks
Some people experience mild side effects, such as headaches and itching. There are not major safety concerns with short-term use in adults; the effects of long-term use are unknown.

Editor's Note: This article also appeared in the December 2019 issue of Consumer Reports.