Gossypol is a polyphenol C₃₀H₃₀O₈ derived from the cottonseed plant (genus Gossypium, family Malvaceae) used as a male oral contraceptive in China. Its efficacy is comparable to the female birth control pill.

A 1929 investigation in Jiangxi showed correlation between low fertility in males and use of crude cottonseed oil for cooking. The compound causing the contraceptive effect was determined to be gossypol.

In the 1970s, the Chinese government began researching the use of gossypol as a contraceptive. Their studies involved over 10,000 subjects, and continued for over a decade. They concluded that gossypol provided reliable contraception, could be taken orally as a tablet, and did not upset men's balance of hormones.

However, gossypol also had serious flaws. Between 5 and 25 percent of the men remained azoospermic up to a year after stopping treatment. The longer the men had taken the drug and the higher their overall dosage, the more likely the men were to have lowered fertility or to become completely infertile.

The studies also discovered an abnormally high rate of hypokalemia among subjects. Hypokalemia—low blood potassium levels—is usually the result of kidney malfunction and causes symptoms of fatigue, muscle weakness, and at its most extreme, paralysis. In addition, about 7% of subjects reported effects on their digestive system, and about 12% increased fatigue. Most subjects recovered after stopping treatment and taking potassium supplements. A later study showed that taking potassium supplements during gossypol treatment did not prevent hypokalemia in primates.

In 1986, the Chinese stopped research because of these side effects. In the mid-1990s, the Brazilian pharmaceutical company Hebron announced plans to market a low-dose gossypol pill called Nofertil, but the pill never came to market. Its release has been indefinitely postponed due to unacceptably high rates of permanent infertility. Trials involving multiple years of use have consistently reported sterility rates of 10 to 20%.

In 1998, the World Health Organization's Research Group on Methods for the Regulation of Male Fertility recommended that research should be abandoned. In addition to the other side effects, the WHO researchers were concerned about gossypol's toxicity: the toxic dose in primates is less than 10 times the contraceptive dose. This report effectively ended further studies of gossypol as a temporary contraceptive, but research into using it as an alternative to vasectomy continues in Austria, Brazil, Chile, China, the Dominican Republic, and Nigeria.