A capsule of mixed fatty acids could provide monthly relief for women against pre-menstrual tension (PMT).
Scientists hope the supplement could reduce the emotional and physical symptoms that regularly frustrate millions of women and their partners.
During trials women who took the 2g capsules over a six-month period reported that their symptoms became much less severe over time.
Around 80% to 95% of women of reproductive age are affected by PMT, with a third of them suffering disruption to their routine activities as a result.
For up to 15% of those with PMT, their symptoms are severe enough for it to be classed as a disabling condition called pre-menstrual dysphoric disorder (PMDD).
Brazilian researchers revealed that PMDD has been known to lead to serious mental problems requiring psychiatric help, even leading to suicide. Their findings were published in the journal Reproductive Health.
The capsules contain a mix of oils including gamma linolenic acid, oleic acid and linoleic acid, combined with vitamin E.
They were tested on a group of 120 women aged 16 to 49 with diagnosed PMS or PMDD, who were either given the treatment or a "dummy" placebo.
The women were asked to rate a list of symptoms according their severity, with each given a score from zero to three. Each month, the combined scores were added up.
Over six months, those taking a 2g dose of the oils saw their scores drop from 98 to 28.
The placebo group also experienced a reduction, but it was much smaller.
Lead researcher, Dr Edilberto Rocha Filho, from the Federal University of Pernambuco, Brazil, said: "The negative effect of PMS on a woman's routine activities and quality of life may be significant, in addition to the repercussions on economic costs resulting predominantly from a reduction in productivity.
"Essential oil capsules can now be said to show much promise as a treatment."