Currently, the only forms of contraception widely available to men are vasectomy and condoms. Photo by 3dmotus/Shutterstock

OSAKA, Japan, Oct. 2 (UPI) -- Researchers in Japan may have found a method for reliable, reversible male contraception by blocking a protein in mice using two immunosuppressive drugs typically given to organ transplant patients.

While the two drugs are not being recommended for use as contraceptives, researchers said the finding may lead to an option for men other than vasectomy or condoms.


"It is important that we find an effective and reversible contraceptive option to allow men more control over their own reproductive futures," Masahito Ikawa, a researcher at Osaka University, told HealthDay. "The findings of this study may be a key step to giving men that control."

The researchers found a version of the protein calcineurin that is present only in sperm -- other forms of it exist in the body, playing a role in the immune system -- which they thought played a role in male fertility.

First breeding mice whose genes for the protein had been "knocked out," the researchers found mice sperm had trouble generating the movement needed to swim to an egg for fertilization.

Having seen this, the mice were then treated with cyclosporine A and tacrolimus, immunosuppressive drugs used with transplant patients to prevent their bodies from rejecting new organs. Within 5 days, the mice were infertile, despite continuing to have sex. When the researchers stopped the treatment, it took about a week for the mice to become fertile again.

The researchers said they do not recommend people using the drugs as contraceptives. The new understanding of calcineurin will fuel work to develop a drug meant to target the protein specifically to prevent pregnancy.

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The study is published in the journal Science.