Period pain is a common complaint
Acupuncture may be an effective way of easing severe period pain, a South Korean review of 27 studies suggests.
Researchers said there was "promising evidence" for acupuncture in treating cramps, but that more work was needed.
In the British Journal of Obstetrics and Gynaecology, they noted two studies found little difference between real and sham acupuncture in treating pain.
Acupuncture is a less contentious form of complementary medicine than some, but its value is still disputed.
Period pain can be severe in some women and may be accompanied by nausea, diarrhoea, migraine and backache. Common treatments include pain killers, applying heat and exercise - although a recent study questioned the efficacy of the latter.
This latest review involved 27 studies - which included nearly 3,000 women. They addressed a variety of forms of acupuncture - from classical to acupoint injection.
Traditional acupuncturists insert needles in acupuncture points located along what they describe as "energy meridians" - a concept for which many scientists say there is no evidence. Sham acupuncture places needles away from these points.
It is not clear whether either form alleviates pain as a result of the placebo effect - the very ritual of undergoing acupuncture - or cause subtle changes in the nervous system and brain activity which can be beneficial.
Nice backs needles
The analysis by the team from Kyung Hee Medical Centre found that patients with severe period pain reported a greater reduction in their symptoms when using acupuncture compared with pharmacological treatments.
But they stressed there were methodological flaws in some studies, and that the findings did need to be interpreted with caution. Nevertheless, there was "promising evidence", they wrote.
In the UK, the National Institute for Health and Clinical Excellence (Nice) has backed the use of acupuncture in the treatment of low back pain - a move welcomed by some but criticised by those who say there is little evidence for its efficacy.
The editor-in-chief of the BJOG, Professor Philip Steer, noted that some women had period pain, also known as primary dysmenorrhoea, so badly they were "unable to function normally".
"Women with primary dysmenorrhoea should consult their GPs or gynaecologists on the best treatment available to them. Complementary therapies should not be used exclusively, at the expense of conventional treatment, unless significant improvements have been made and your doctor tells you otherwise."