HIV/AIDS is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. After the initial infection, a person notices no symptoms or may experience a short period of influenza-like illness. As a rule, this condition is followed by a long incubation period without any symptoms. If the infection progresses, it affects the immune system more, increasing the risk of common infections such as tuberculosis and other opportunistic infections that are rare in people with normal immune function. These late symptoms of infection are called acquired immunodeficiency syndrome (AIDS). This stage is also often associated with unintentional weight loss.

HIV is invaded mainly through unprotected sex (including anal and vaginal sex), transfusion of infected blood, hypodermic needles, and from mother to child during pregnancy, childbirth or breastfeeding. Some body fluids, such as saliva, sweat, and tears, do not transmit the virus. There is practically no risk of virus transmission through oral sex.

Treatment of HIV infection with antiviral drugs and immunomodulators helps improve the condition of patients and prolong their lives. All the most effective drugs suppress appetite, which is especially undesirable in the case of wasting syndrome, which is observed in most AIDS patients. To increase appetite, Marinol or medical marijuana is used in the USA, Canada, and the UK.
A study conducted in the USA showed that 70 % of patients who took Marinol did not lose weight but also put on weight.