Smoking cannabis suppresses the immune system and so, may increase the risk of cancer, claims a new US study.
Scientists believe the drug triggers the production of cells that weaken the body's resistance to cancer, reports the Scotsman.
The study found that cannabinoids - the active compounds in cannabis - activated biological pathways to generate "massive numbers" of the cells, known as myeloid-derived suppressor cells (MDSCs). These are special immune cells that act as a safety brake on the immune system.
They suppress immune responses to prevent them getting out of control, but in so doing are thought to promote cancer growth.
"These results raise interesting questions on whether increased susceptibility to certain types of cancers or infections caused from smoking marijuana results from induction of MDSCs," said lead researcher Dr Prakash Nagarkatti, from the University of South Carolina.
"MDSCs seem to be unique and important cells that may be triggered by inappropriate production of certain growth factors by cancer cells or other chemical agents such as cannabinoids, which lead to a suppression of the immune system's response.
"Marijuana cannabinoids present us with a double-edged sword. On one hand, due to their immunosuppressive nature, they can cause increased susceptibility to cancer and infections. However, further research of these compounds could provide opportunities to treat a large number of clinical disorders where suppressing the immune response is actually beneficial," Dr Nagarkatti said.