Cancer patients and survivors who felt tired or sluggish reported feeling noticeably better after taking ginseng supplements for two months, in a new study.

"Nearly all patients with cancer can suffer from fatigue at some point; either at diagnosis, during treatment and even after treatment, and (fatigue) can linger for several years," said lead author Debra Barton, from the Mayo Clinic in Rochester, Minnesota.

"The issue with cancer-related fatigue is that it can be a profound fatigue that is not relieved by sleep or rest and that it can significantly impact the ability of people to accomplish the things they are used to doing every day," Barton said in an email.

Ginseng had shown promise for fatigue in earlier studies as well, researchers said.

Tired cancer patients and survivors often turn to that and other dietary supplements such as Coenzyme Q-10, L-Carnitine and guarana, but not all are supported by evidence.

To look more closely at the effects of ginseng, Barton and her coauthors split 364 people with cancer-related fatigue into two groups. People in one group took 2,000 milligrams of Wisconsin ginseng daily for eight weeks; those in the other group took placebo capsules.

Participants reported their fatigue on a specialized questionnaire. Researchers then weighted those answers on a 100-point scale, where higher scores indicate more energy. Both groups started with an average score around 40.

After eight weeks, the ginseng group reported a 20-point score increase, on average, compared to a 10-point improvement for the placebo group, according to results published in the Journal of the National Cancer Institute.

That's more than enough change to be noticeable in daily life, according to the scale.

Of the 364 people enrolled at the start of the study, 80 dropped out before the eight-week mark. Although that's a high number, dropout rates were similar in each group - so the results shouldn't be affected, Barton said.

Side effects such as nausea, vomiting and anxiety were not any more common among people taking ginseng.

"Ginseng is interesting because it acts on inflammation, and we think inflammation explains cancer-related fatigue," said Catherine Alfano, deputy director of the office of cancer survivorship at the National Cancer Institute in Bethesda, Maryland.

The results of this trial are promising, but they aren't enough to recommend that doctors suggest this supplement to patients, she said.

A bottle of 100 capsules containing 500 mg of Wisconsin ginseng each costs about $10 at a drugstore. Dietary supplements such as ginseng are not regulated by the U.S. Food and Drug Administration.

"There may be ginseng available in the local stores that is very different from what this study used, and some that is quite similar," Barton said. "There are different types of ginseng, different strengths (doses) and since it is a plant, (it) has to be grown, picked, processed and manufactured to get from field to store."

It's difficult for people to tell what exactly they're getting when they purchase supplements, she said.

Also, it is not yet known how ginseng may interact with drugs or with cancer treatment itself - another reason patients should not go out and use it to medicate themselves just yet, said Alfano, who wasn't involved in the new study.

More research needs to be done to determine why ginseng seemed to have stronger anti-fatigue properties for people undergoing cancer treatment than after treatment, she said.

"Cancer-related fatigue can be really profound in some cases," she said. "People really want answers."

There is a great deal of evidence that a simple exercise program, even just regular walking, can work against cancer-related fatigue, and that's what Alfano said she would most strongly recommend to patients.