Another experimental form of male contraception, which suppresses the production of sperm, was reported in 2001. The regimen tested in the study includes a form of the male sex hormone testosterone, testosterone undecanoate, and norethisterone enanthate (NETE), a hormone used in some female contraceptives. The contraceptive injections were given every 6 weeks, not every week or two as in some other male contraceptives being tested. By the end of the study, sperm production had completely stopped in 13 of the 14 men receiving the hormone combination but in only 7 of the 14 taking testosterone alone. The injections did affect cholesterol levels, raising LDL ("bad") cholesterol and lowering HDL ("good") cholesterol, and caused other more minor side-effects.
Sperm counts are falling, apparently due to synthetic chemicals in plastics and certain pesticides that act like female hormones and are ingested with foods.