1858 -- Discovered in 1858, the inventor drank some, got the Aztec-two-step, and declared it a laxative.

Phenolphthalein was the main component in numerous over-the-counter laxatives, including Ex-Lax and Feen-A-Mint, for most of the 20th century.

1958 -- 100 years after discovery, the US Food and Drug Act was passed and the new FDA declared all drug products currently in commerce as generally recognized as safe (GRAS).  This included phenolphthalein.

1975 -- The U.S. Food and Drug Administration (FDA) classified phenolphthalein as “safe and effective” in 1975.

1992 -- Studies finished and reported in 1992 showed multiple cancers at multiple sites. A 2-year feeding study in rodents found increased incidences of neoplasms of the ovary, adrenal gland, kidney, and hematopoietic system in treated animals.

1997 -- The FDA proposed that phenolphthalein be reclassified as “not generally recognized as safe and effective”. Phenolphthalein by this time had also been found to be genotoxic, to cause oxidative damage, and to bind to estrogen receptors.

Feb 1, 1999 · FDA's final rule banning the use of phenolphthalein in OTC stimulant laxatives based on safety concerns was published in the Jan. 28 Federal Register. The rule is effective immediately – 7 years after the studies showed it was a carcinogen.