Vasectomy is a highly effective form of male contraception, but is difficult to reverse. Therefore, recent research has explored the concept of reversible forms of contraception that target the vas deferens, the tube that transports mature sperm to the urethra.
Researchers tested the effect of one of these contraceptives, Vasalgel — a high molecular weight polymer consisting of 25% styrene maleic acid in dimethyl sulfoxide injected into the vas deferens — on 16 adult male rhesus monkeys. The monkeys were then returned to enclosures with reproductive females for at least one breeding season.
Over a mean period of 1.2 years, no females housed with the Vasalgel-treated monkeys became pregnant, even those co-housing for two full breeding seasons. The rate of complications was similar to an age-matched group of vasectomy-treated monkeys.
Reporting their findings in Basic and Clinical Andrology
(online, 7 February 2017), the researchers say further study is needed to explore the possibility of reversal by flushing the gel from the vas deferens.
 Colagross-Schouten A, Lemoy M-J, Keesler RI et al. The contraceptive efficacy of intravas injection of Vasalgelâ¢ for adult male rhesus monkeys.Basic Clin Androl 2017; 27: 4 doi: 10.1186/s12610-017-0048-9