Clinical trials begin only after preliminary studies in the laboratory, and with animals, have shown that the drug is safe enough to be taken by people. Clinical trials in people are usually conducted in three steps or phases:

Phase I

Phase I trials test the treatment in only a few people (usually healthy volunteers who are not HIV-positive or those with HIV who are not on other medications) to learn whether it is safe to take, and to find the maximum safe dose. If you enrol in a phase I trial you may have to spend some time in hospital for close monitoring of drug levels in your blood. There are usually no direct health benefits from participating in a Phase I trial.

Phase I/II

Phase I/II trials test the treatment in up to few hundred HIV-positive people to find the most effective dose.

Phase II

Phase II studies assess whether the treatment is active against the disease in the short term by looking for changes in viral load and CD4 count. If the treatment is not active, no more trials will take place. Phase II trials usually last for at least six months. If you enrol in a Phase II study you will need to attend the clinic on a regular basis for blood tests and other monitoring.

Phase III

Phase III trials test the treatment in a larger group of people, often at many different clinics or hospitals. Usually the drug is given in a dose that has been found to be safe enough for most people in Phase I or II trials, and is thought to be active against the disease. These trials compare the new treatment either with a treatment already in use or, occasionally, with an inactive look-alike pill called a placebo.

Phase III trials usually last for at least twelve months, and also require a commitment to regular clinic attendance.