A natural substitute for the morning after pill has been found in olives.
Eating handfuls of olives will not prevent pregnancy, but a chemical found within them can stop a sperm from reaching an egg, the Daily Mail reports.
The natural compound, also found in grapes and mangos, could replace the morning after pill if taken within five hours of unprotected sex.
It could also become the first unisex pill, able to be taken by both men and women without the current side-effects of heart disease, blood clots and depression.
The chemical, lupeol, works by stopping the sperm's "power kick", where its tail is whipped up forcefully to propel it towards and into the egg. Another chemical, primisterin, which is found in the thunder god vine used in Chinese medicine, has the same effect.
Researchers at the University of Berkeley in the US say it could be available within two years for women to take before or after sex, and within four years for men.
Co-author Dr Polina Lishko said: "It is not toxic to sperm cells - they still can move. But they cannot develop this powerful stroke, because this whole activation pathway is shut down. This is a potentially safer morning after pill, regular pill, and a future male contraceptive. Essentially it is a future version of a unisex contraceptive."
Fertility expert Allan Pacey, professor of andrology at the University of Sheffield, said:
"This is probably one of the most innovative approaches to male contraception, allowing men to take equal responsibility for family planning that we have seen in a long time.
"Scientists have been tinkering with different kinds of hormonal contraceptives for men for 30 years and they have not yet got them to marketplace, so we really need a new kind of approach like this."
The Pill, which stops women from ovulating, comes with a slightly increased risk of high blood pressure and blood clots.
Existing trials of a male contraceptive, while found to be as effective as the Pill, have caused side effects of acne, muscle pain and emotional disorders.
The authors of the latest study, published in the journal Proceedings of the National Academy of Sciences, say the two plant compounds could provide an alternative, in the form of a pill or skin patch.
Prof Pacey said: "This paper shows clear proof of principle that these natural compounds can affect sperm. And because they act specifically on sperm you wouldn't expect to see the kind of side-effects that have been observed in the hormonal male contraceptives that have been trialled so far."