Different formulations of AZT, courtesy MastCell, via Wikipedia
Zidovudine or azidothymidine, better known as AZT, is an antiretroviral drug used first in the treatment of HIV/AIDS. AZT is a reverse transcriptase inhibitor, which inhibits the only reproduction of viral genetic material. Genetic material in a human cell is stored in the form of DNA, while HIV stores genetic material as RNA. This RNA must first be converted to DNA by reverse transcriptase in order to be inserted into the human genome. AZT inhibits this process, thus delaying the progression of the disease. However, over time, HIV can mutate and become immune to AZT.
AZT has serious side effects, including nausea and liver and heart damage.