The existing drugs have worked wonders for people with HIV, and over the past 5 years have dramatically reduced the number of AIDS deaths in the United States and other countries where people have access to them. But they also have limitations. They are not easy to take correctly. Patients have to follow complicated and strict dosing schedules. Once the virus mutates to resist one drug in a class, it may be able to resist all the drugs in that class.
Patients experience sometimes severe side effects , and toxicity develops over long-term use.