Therefore, a high sensitivity to allopregnanolone before menstruation results in mood swings and heightened emotions before menstruation.

The study, by doctor Erika Timby at the Umeå 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.

Dr Timby said: "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.

"Greater knowledge of the underlying mechanisms of pronounced PMS can ultimately provide clues for new methods of treatment."