The chemical compound in cannabis, THC, appears to be able to damage and weaken the most common strain of the HIV virus.
Before you light up a spliff, though, this is only a preliminary result reached under laboratory conditions, and further research will be needed.
THC, or tetrahydrocannabinol, is the main psychoactive ingredient in cannabis -- it's the chemical that gets the user stoned. Synthetic versions of it have been developed for research purposes, and it's this that was used to attack the HIV-1 virus, which represents the vast majority (more than 90 percent) of all HIV types.
Source: Wired UK. Read full article. (link)