Half took a placebo and the other half took capsules containing 2,000 milligrams of pure, ground, American ginseng root daily.
At the start of the study, everyone was asked to rate how fatigued they felt on a 100-point scale; the average score was about 55 points.
Four weeks into the study, there was not a big difference in scores between the two groups. But by eight weeks, fatigue scores improved by 20 points in the ginseng group vs. only 10 points in the placebo group.
"People taking ginseng reported feeling less pooped, worn out, and sluggish than those taking placebo," says researcher Debra Barton, PhD, of the Mayo Clinic Cancer Center in Rochester, Minn.
Ginseng appeared to be as safe as placebo, at least over the eight-week period, she tells WebMD.
Based on the findings, "I would recommend ginseng for patients with cancer-related fatigue," Barton says.
One caveat: Since supplements are not regulated like drugs by the government, you can't always be sure of the purity of a product. So make sure you buy from a reputable company whose labels you can trust, she says.
That's especially important with ginseng because it is sometimes processed using ethanol, which can give it estrogen-like properties that actually stimulate the growth of breast cancer cells, Barton says.
"The label should read that it is pure ground root of ginseng as opposed to an extraction," Barton says.
The findings were reported here at the American Society of Clinical Oncology meeting.
More Study Needed
Sriram Yennu MD, of the University of Texas M.D. Anderson Cancer Center in Houston, says further and longer study is still needed to confirm ginseng's safety for people with cancer.
"We can tell patients it is safe to use for eight weeks and may benefit. But no one should self-prescribe [the herbal supplement] at this point," he tells WebMD.
Still, the findings are "exciting because there are no or limited choices" for treating cancer-related fatigue, Yennu says.
Exercise is the only intervention that has been shown to help relieve the fatigue, Barton says. "But people with cancer often don't have the energy to exercise," she points out.
In traditional Chinese medicine, ginseng is seen as a natural energy-booster that "helps the body deal with physical stress and balance things out," Barton says.
Experiments in the lab and in animals suggest it works as an anti-inflammatory or by controlling levels of stress hormones that the body makes when under physical or psychological stress, she says.
The new study builds on previous work at the Mayo Clinic that showed that about one-fourth of people with cancer-related fatigue said they felt "moderately better" or "much better" after taking 1,000-milligram or 2,000-milligram ginseng tablets, compared with 10% taking placebo pills.
People in the current study took the 2,000 milligrams of ground Wisconsin ginseng root as two capsules separately before noon. Barton plans to test higher doses for relieving fatigue even more quickly.
The most common side effects over eight weeks of treatment were nausea, experienced by 5% of people taking ginseng and 4% on placebo group. About 4% on ginseng reported loose stool vs. 3% on placebo.
Serious side effects that typically require hospitalization affected similar numbers of people in both groups: 8% on ginseng and 6% on placebo, a difference so small it could be due to chance. Serious side effects included dizziness and low blood cell counts.
Barton says a month-supply of 2,000-milligram capsules costs about $30.
Len Lichtenfeld, MD, deputy chief medical officer of the American Cancer Society, cautions that anyone with cancer taking any type of supplements should be sure to tell their doctors.
"Some can interfere with the cancer treatment," Lichtenfeld says.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.