The U.S. Food and Drug Administration’s approval in 1987 of zidovudine, more widely known as AZT, was a breakthrough in the treatment of HIV/AIDS. While not able to cure the disease, the drug was found to prolong the lives of AIDS patients. It also was the first of the so-called nucleoside reverse transcriptase inhibitors, a group of antiretroviral drugs that became a cornerstone of HIV/AIDS therapy. Owing to these drugs—and perhaps most significantly to increased access to these drugs in countries worldwide—the annual number of deaths from AIDS declined in the early 21st century.