Taking the Pill could be a simple solution for thousands of women who suffer "time-of-the-month" pain, a study has shown.
Scientists say they now have "convincing evidence" that the combined oral contraceptive pill alleviates symptoms of painful menstrual periods.
Many GPs already prescribe the Pill "off label" - for a purpose it is not licensed for - to help women plagued by period pain.
The research shows that while period pain declines with age, oral contraceptives have an independent and greater pain-relieving effect.
Swedish doctors questioned three groups of women who reached the age of 19 in 1981, 1991 and 2001.
Each group included around 400 to 520 women who provided information about their menstruation history and contraceptive use. Five years on, at the age of 24, they were assessed again.
Two different scales were used to grade period pain, or dysmenorrhoea, reported by the patients. One, the verbal multidimensional scoring system (VMS), rated pain as non-existent, mild, moderate or severe. The other, the visual analogue scale (VAS), allowed the patient to grade her pain on a 10 centimetre line that started with "no pain at all" and ended with "unbearable pain".
Lead researcher Dr Ingela Lindh, from Gothenburg University, said: ""We found that combined oral contraceptive use reduced dysmenorrhoea by 0.3 units, which means that every third woman went one step down on the VMS scale, for instance from severe pain to moderate pain, and which meant that they suffered less pain, improved their working ability and there was a decrease in the need for analgesics. On the VAS scale there was a reduction in pain of nine millimetres."
Increasing age also reduced the severity of period pain, but not as much, according to the findings reported in the journal Human Reproduction. Childbirth also appeared to have some pain-relieving effect.
An estimated 50% to 75% of young women suffer from dysmenorrhoea. Period pain can have a serious impact on their lives, causing absenteeism from school and work and interfering with daily activities for several days each month.