A male contraceptive gel has been found to be effective in rhesus monkeys, providing long-term and reliable birth control in 16 adult male monkeys.

The breakthrough technique involves injecting Vasalgel into the duct which conveys sperm from the testicle to the urethra (or vas deferens) – and scientists believe it could offer a reversible alternative to vasectomy. However, trials in humans are still some way off.

Animal testing

Vasagel had previously been trialled in rabbits with reliable results. Next, researchers led by Catherine VandeVoort from the California National Primate Research Centre trialled the technique on monkeys.

The study, published in Basic and Clinical Andrology, showed how 16 male adult rhesus monkeys were given Vasalgel injections. After a week of recovery, they were returned to outdoor housing with breeding females. Males that had received the treatment had no conceptions throughout at least one breeding season. Seven were still infant-free after two years.

rhesus monkey
Rhesus monkeys at the California National Primate Research Centre California National Primate Research Centre

There was one minor complication where sperm granuloma developed. This is where there is a hard build-up of sperm in the vas deferens – a common complication following a vasectomy in humans.

How does it work?

Vasalgel is a non-pharmaceutical agent that forms a hydrogel that can be injected into the vas deferens. The gel fills the internal cavity of the vas deferens. This forms a mechanical barrier, preventing the movement of sperm.

Would it work in humans?

As well as controlling monkey populations, the gel could one day have human applications. VandeVoort said it shows promise as an alternative to vasectomy as it has the added benefit of potentially being more easily (and successfully) reversible.

But testing of such a procedure is still some way off.

Commenting on the study, Adam Balen, Chair of the British Fertility Society said: "This is an interesting technique that achieves a reversible 'vasectomy' by blocking the passage of sperm with a substance that later can be flushed out. If free of side effects then this novel approach has the potential for great promise as a male contraceptive. It is essential to know that the reversibility remains, irrespective of the duration of use."

Allan Pacey, professor of andrology at the University of Sheffield, added: "The idea of trying to replace the traditional method of vasectomy by inserting a gel into the tube which carries sperm from the testicles to the penis at ejaculation is not a new one. However, we haven't seen much progress in developing the idea in recent years, so this study is a useful step in the right direction.

"The study shows that, in adult male monkeys at least, the gel is an effective form of contraception. But in order for it to have a chance of replacing the traditional surgical method of vasectomy, the authors need to show that the procedure is reversible and its reassuring that apparently such studies are ongoing.

"It's interesting that there has been very little commercial interest from pharmaceutical companies in this kind of a approach and so the idea of a social venture company to develop the idea is intriguing. I would imagine there is a worldwide market for a new male contraceptive, but trials in humans and more long-term safety data are required before we will know if it is a success."