Could Men Take a Pill Before Sex To Stop Sperm? Scientists Move Closer to Human Testing
An experimental pill designed to temporarily stop sperm from swimming has received funding for further development. Researchers at Weill Cornell Medicine hope it could work within 30 minutes and wear off after six to eight hours, but its effectiveness and duration of action have not been established in humans.
About 40 per cent of US pregnancies are unplanned, according to the Centers for Disease Control and Prevention. Male options are mainly condoms and vasectomy, so contraception largely falls to women.
About a third of women stop hormonal contraception within a year, mostly because of side effects, said Jean-Ju Chung, an associate professor at Yale University. Stopping while still wanting to avoid pregnancy is a leading route to unintended pregnancy.
How the Drug Works
The drug targets an enzyme in sperm called soluble adenylyl cyclase (sAC). Dr Jochen Buck said sperm need the enzyme to become motile and undergo capacitation, a process that enables them to fertilise an egg. Dr Lonny Levin said men born without it are infertile.
The inhibitors block sAC activity, preventing sperm from swimming effectively after ejaculation. As the drug's effects wear off, fertility may return, although reversibility must be established for the candidate being developed.
Chung, who studies cellular and molecular physiology, said most male candidates target sperm production. That takes about two and a half months, so those drugs are slow to work and reverse.
By contrast, drugs that block sAC act on sperm that already exist, so they could work faster than treatments that suppress sperm production. Their duration of action and reversibility remain unproven in humans.
The Eunice Kennedy Shriver National Institute of Child Health and Human Development awarded a multimillion-dollar, four-year grant to advance development of the candidate towards initial human safety studies. The funding is the third grant awarded to pharmacologists Dr Jochen Buck and Dr Lonny Levin since 2020.
Condoms and Hormonal Alternatives
External condoms help reduce the risk of sexually transmitted infections as well as pregnancy, whereas this experimental pill is not known to offer STI protection. A review of male contraception puts typical-use condom failure at 13 per cent.
Hormonal male candidates are further along. The same review lists weight gain, acne, mood changes and reduced libido as commonly reported side effects.
A UT Southwestern urologist said a 28-day study of 82 men tested the hormonal pill dimethandrolone undecanoate. Mild side effects, also reported by some men on placebo, included acne, headaches and weight gain of 5lb or less. Long-term effects are unknown.
Safety Questions and Next Steps
For the sAC pill, animal studies, even at very high doses, have shown no side effects, the researchers say. That has yet to be tested in men, so safety in people is the central question for the next phase of work.
Steven W. L'Hernault, a professor of biology at Emory University, said he has some concerns because sAC is also found beyond the testis, including the eye. A male contraceptive must be exceedingly safe, he said, but he praised the team as careful.
L'Hernault added that researchers must show the compound stays active once semen is inside the female reproductive tract. If sperm regain movement there, fertilisation could occur.
Sperm can survive for up to five days in the female reproductive tract under favourable conditions. This raises questions about whether a contraceptive effect lasting only several hours would provide sufficient protection against pregnancy.
The researchers hope to begin human tests within two years, after animal safety testing. They expect treated sperm to twitch rather than swim under a microscope.
Trials with couples would take several years to check whether animal findings hold in men. Levin said a sellable drug is still some way off.
Chung urged patience, noting that phase one is a small safety study and that the field has been set back before by promises of a male pill within five years. Trials should enrol female partners in their own right, she said.