Upjohn Company, one of Pfizer’s acquisitions, debuted the birth control shot in the 1950s. Upon injection, the synthetic progestoerone cocktail is supposed to suppress ovulation and prevent pregnancy in women for up to three months at a time.
The U.S. Food and Drug Administration initially approved the drug for limited contraceptive use in 1974. Widespread concern about cancer risks, however, forced the FDA to deny it a "general marketing licence" just four years later in 1978.
By 1992, however, the FDA had rubber-stamped Depo-Provera, which was increasingly prescribed to women off-label as birth control under the condition that its manufacturer would conduct "post-market studies of the risk of osteoporosis."
It wasn’t until years after that Depo-Provera’s official label would disclose a warning about "loss of bone mineral density" and recommend less than two years’ use.