Cannabis is one of the most widely used drugs of abuse and is already believed to suppress immune functions and to make users more susceptive to infections and some types of cancer.

The active compounds of cannabis, including THC (delta-9 tetahydrocannabinol), which is already used as pain relief, can trigger myeloid-derived suppressor cells (MDSCs) according to Prakash Nagarkatti and co-workers, University of South Carolina, USA.

It is believed that MDSCs may suppress the immune system against cancer therapy, promoting cancer growth as MDSCs are seen to increase in cancer patients. In a related study Christian A. J. Vosshenrich, Institut Pasteur, Paris, France, and co-workers demonstrated that growing cancer cells produce interleukin-1β, which also triggers MDSCs.

While this research provides further evidence for the link between smoking cannabis and cancer, it also opens up possible news routes for the treatment of autoimmune disorders where suppressing the immune response is desired.

• Cannabinoid receptor activation leads to massive mobilization of myeloid-derived suppressor cells with potent immunosuppressive properties
  V. L. Hegde, M. Nagarkatti, P. S. Nagarkatti,
  Eur. J. Immunol. 2010, 12, 3358–3371.
  DOI: 10.1002/eji.201040667

• IL-1β regulates a novel myeloid-derived suppressor cell subset that impairs NK cell development and function
  M. Elkabets, V. S. G. Ribeiro, C. A. Dinarello, S. Ostrand-Rosenberg, J. P. Di Santo, R. N. Apte, C. A. J. Vosshenrich,
  Eur. J. Immunol. 2010, 12, 3347–3357.
  DOI: 10.1002/eji.201041037