A compound tested as a cancer drug in the 1960s failed and drew little interest for two decades until the HIV epidemic arrived. Researchers tested AZT against the virus and found it blocked replication, and in 1987 it became the first antiretroviral drug approved in the United States to treat AIDS.

In 1964, a chemist in Detroit made a molecule to attack cancer. It didn’t work. Twenty-three years later, that same molecule became the first drug approved in the United States to treat AIDS.

We are not clinicians, virologists, or pharmacologists, and nothing here is medical advice. This is history reporting on how one compound moved through the research system, not guidance for anyone managing HIV today. Treatment has changed enormously since 1987, and decisions about it belong with a qualified doctor.

The chemist was Jerome Horwitz. As Samuel Broder’s review in Antiviral Research records, Horwitz and his colleagues synthesized AZT in 1964 with National Cancer Institute grant support as a potential anticancer agent. The compound, also called azidothymidine or zidovudine, failed in the cancer-drug screening of the time.

He didn’t even patent it, HIV i-Base reported. The same account, recalled his description of the shelved molecules as “a very interesting set of compounds that were waiting for the right disease.”

That line reads differently with hindsight. At the time, the compound had failed to deliver the anticancer effect its researchers wanted. Its eventual success would depend on testing it against another target.

AZT wasn’t quite forgotten. In 1974, Wolfram Ostertag and colleagues reported that it suppressed a mouse leukemia virus in cell culture. The virus belongs to a family called retroviruses, which copy RNA into DNA using an enzyme called reverse transcriptase.

The finding did not immediately produce a human treatment. In 1974, human retroviruses had not yet been definitively identified, and their role in human disease had not been established.

The useful property was on record before AIDS was recognized. What was missing was evidence that it could help against a human infection, and a research program capable of testing that possibility.

The context changed brutally in the early 1980s, when AIDS emerged and HIV was identified as its cause. HIV is a retrovirus. At the National Cancer Institute, oncologist Samuel Broder and his colleagues Hiroaki Mitsuya and Robert Yarchoan searched for compounds that inhibited viral growth in the laboratory, as the institute’s account describes.

Among the candidates was AZT, the compound Horwitz had synthesized in 1964. NCI researchers tested potential drugs for their ability to suppress HIV and protect human cells, finding AZT active against the virus in February 1985.

The researchers had focused on reverse transcriptase. Once activated inside cells, AZT interferes with that enzyme and terminates growing viral DNA chains. The broad idea of disrupting DNA copying had found a useful application.

What followed was fast. A trial involving nearly 300 people was stopped early because survival was significantly better in the AZT group. As Time recounts, there had been one death among those receiving AZT and 19 among those receiving placebo. On March 19, 1987, the FDA approved it, making it the first antiretroviral drug cleared in the United States to treat AIDS.

AZT was not a cure. Used alone, its benefits were limited by emerging resistance. It could also cause serious side effects, including severe anemia.

What it helped establish was the principle that HIV could be treated, supporting the development of further drugs and combinations. AZT remains approved, but the National Institutes of Health’s current drug information says it is no longer commonly used or recommended to treat adults and adolescents. When used for HIV treatment, it is combined with other medicines.

What we take from a drug developed for another disease

The comfortable reading is that failure is never final and good science eventually finds a use. We’re wary of that. AZT’s history depended on published chemistry, further experiments, collaboration and an urgent new medical problem. It was not simply a forgotten vial rescued from a shelf.

So the thing we keep coming back to isn’t that failure pays off. It’s the value of keeping unsuccessful research accessible, and of testing old candidates against new targets. Horwitz’s compounds really were waiting for another use. Finding it took much more than waiting.