A contraceptive pill for men could transform the sex lives of millions of people all over the world, British scientists believe.
Researchers made a major breakthrough in developing the treatment, which involves switching off the 'wiggle' in sperm tails.
The group claim they have found a way to temporarily deactivate sperm, immobilising them and therefore leaving them unable to fertilising a woman's egg.
“We are basically designing peptides that can alter the physiology of sperm," Dr Sarah Jones from the University of Wolverhampton said.
“We hope to develop something that will be clinically useful and can be taken forward in the future.”
It's thought the contraceptive could also be taken in the form of a nasal spray or skin implant, with the effects wearing off in several days.
It would offer men an alternative form of birth control, other than condoms or a vasectomy, and could be taken moments before intercourse.
"The results are startling – and almost instant," lead researcher Professor John Howl said.
"When you take healthy sperm and add our compound, within a few minutes the sperm basically cannot move.
"This is a totally unique approach – nobody else has ever done this before."
The development is still in the testing stage, but if everything goes to plan, it could be available by 2021.