Researchers recruited HIV-infected patients who had been taking protease inhibitors for at least 2 months. All had smoked marijuana before and had stable viral loads for at least 4 months. They were randomly assigned to receive a marijuana cigarette, a dronabinol tablet, or a placebo tablet three times daily for 21 days. They stayed in a research unit, and researchers observed them taking all treatments. Every 3 days, they had repeated blood samples taken to measure viral loads, and immune function was measured weekly. The researchers then compared these outcomes and weight changes between groups.