The chemical in cannabis that produces a high may help to combat the spread of cancer, research suggests.
Scientists have discovered the active ingredient, delta-9-tetrahydrocannibol can block the spread of gamma herpes viruses.
The viruses are linked to an increased risk of the cancers Kaposis sarcoma, Burkitts lymphoma and Hodgkins disease.
The research, by the University of South Florida, is published in the online journal BMC Medicine.
Gamma herpes viruses are different from the herpes simplex viruses responsible for cold sores and genital herpes.
Among those that have been associated with an increased risk of cancer is Kaposis Sarcoma Associated Herpes Virus.
Once infected, it is almost impossible to get rid of the virus as it lies dormant for long periods within white blood cells.
However, the virus can snap back into action, and suddenly begin to replicate itself, bursting out of the cells to infect others. Once a cell has been infected the chances that it will become cancerous are increased.
The South Florida team found that this sudden reactivation was prevented if infected cells were grown in the presence of THC.