In the 1970s, when my dad might have used a contraceptive pill, prospects seemed better in some ways. Male fertility control was an active research field, with governments backing various ideas to limit overcrowding on Earth. One product he might have been interested in—a non-hormonal drug called gossypol—was being tested on a scale that has never been matched since. At the UN’s 1974 World Population Conference, Elsimar Coutinho, today a famous sex and fertility doctor in Brazil, was promoting the drug, which he was testing on men at the Federal University of Bahia. However, attitudes surrounding sex and reproduction can be unpredictable, and not everyone was convinced of its worth.

“The conference hall was full of women,” Coutinho says on the phone, his gravelly voice matching his website’s picture of a suave doctor with slicked-back grey hair. “I was going to tell them, ‘Now you don’t have to take pills if you don’t want.’” Yet, having determined their own fertility through the contraceptive pill for little more than a decade, his female audience were determined not to relinquish control. “To my surprise, I was shouted down and booed out.”

Despite such reactions, poorer countries with fast-growing populations found gossypol appealing because it could be extracted cheaply from cotton farming waste. Coutinho had first seen its potential while visiting Brazilian farmers who fed cotton plant debris to their bulls. “The bulls were having sex more often, the farmers thought it was good for sexual prowess,” he recalls. But actually, the bulls were not making enough sperm and were therefore still surrounded by receptive, non-pregnant cows—and just doing what came naturally.

From the 1960s onwards, Coutinho worked on contraception with the Chinese government, which in 1972 ran trials with 8,806 men taking gossypol pills. Daily doses successfully reduced the men’s sperm count enough to satisfy the researchers, but side-effects were a cause for concern. One notable problem was that 66 of the men had low potassium in their blood. More importantly, sperm levels in many men didn’t return to normal when they stopped taking the drug.

Researchers therefore conducted tests for years longer, showing in rats that gossypol doesn’t just stop sperm moving, but also damages the lining of epididymis ducts, which store sperm made by the testicles. Eventually, an October 1986 symposium in Wuhan, China—whose sponsors included the Chinese government and the World Health Organization (WHO)—concluded that gossypol was “of little interest.”

“You may call it a problem, but we saw it as a solution,” Coutinho tells me. He felt that the fact it could be irreversible made gossypol a potential alternative to surgical vasectomy. He joined with an international team of scientists to conduct further trials, the last of whose results were published in 2000. They found no problems with potassium, putting the effects seen in China down to poor diet.