HONG KONG (Reuters) - A study involving nearly 3,500 women in several countries suggests that Chinese herbs might be more effective in relieving menstrual cramps than drugs, acupuncture or heat compression.

Australia-based researchers said herbs not only relieved pain, but reduced the recurrence of the condition over three months, according to the Cochrane Library journal.

"All available measures of effectiveness confirmed the overall superiority of Chinese herbal medicine to placebo, no treatment, NSAIDs (non-steroidal anti-inflammatory drugs), OCPs (oral contraceptive pill), acupuncture and heat compression," said lead author Xiaoshu Zhu from the Centre for Complementary Medicine Research at the University of Western Sydney.

Period pain affects as many as 50 percent of women of reproductive age and between 60 percent to 85 percent of teenaged girls, leading to absences from school and work.

While the cause is still under debate, it is believed to be linked to an imbalance in ovarian hormones.

Chinese herbal medicine has been used to treat the condition for hundreds of years and women are increasingly looking for non-drug treatments.

The survey involved 39 trials -- 36 in China, and one each in Taiwan, Japan and the Netherlands.

Participants given herbal concoctions were prescribed herbs that regulated their 'qi' (energy) and blood, warmed their bodies and boosted their kidney and liver functions.

In one trial involving 36 women, 53 percent of those who took herbs reported less pain than usual compared with 26 percent in the placebo group.

But the researchers said more studies were needed because of the relatively small numbers of participants in each of the trials.