Research in to premenstrual syndrome, which affects up to eight percent of women, showed that the affliction was due to a hormone that occurs naturally in the body.
Women suffer the physical and emotional symptoms of PMS depending on their sensitivity to the hormone, allopregnanolone.
The hormone is released in the body after ovulation and during pregnancy, and when changes occur in the course of the menstrual cycle.
Most women are more sensitive to allopregnanolone immediately after menstruation, and less sensitive before. They usually suffer no PMS complaints.
However women who suffer severe symptoms of PMS experience the opposite, a high sensitivity before their period, which may mean they have less ability to adapt to hormonal variations.
Therefore, women with a high sensitivity to allopregnanolone before menstruation experience mood swings and heightened emotions before having their periods.
The study, by doctor Erika Timby at the Umee University, Sweden, is a breakthrough in understanding PMS.
During her doctoral dissertation, women were given allopregnanolone in doses that elevated the amount in their blood to levels normally seen during pregnancy.
Researchers recorded a fatiguing effect in the form of slower eye movement and increased feeling of tiredness.
"We have studied few women, but this is one of the first studies to examine the effects of this particular metabolite from the corpus luteus hormone in humans," the Daily mail quoted Timby as saying.
"Greater knowledge of the underlying mechanisms of pronounced PMS can ultimately provide clues for new methods of treatment," she added.