Cannabis can reduce allergic skin reactions, a new study suggests. The findings may lead to new drugs based on tetrahydrocannabinol (THC), the active ingredient in the plant, to treat allergy and autoimmune disorders.

Andreas Zimmer at the University of Bonn in Germany, and colleagues created a group of mice that lack the receptor for endocannabinoids - forms of THC produced naturally in the body. The team noticed that the mice soon developed a severe skin allergy to the nickel in the metal tags the researchers had fastened to their ears.

Zimmer set up a series of experiments to test the anti-allergy effect of natural and synthetic THC compounds.

Immune suppressant

For example, he exposed the ears of mice with normal endocannabinoid receptors to a chemical irritant called dinitrofluorobenzene (DNFB), which causes a severe skin reaction similar to that caused by poison ivy in humans.

Within a matter of minutes, the amount of an endocannabinoid called anandamide jumped from undetectable levels to about 300 picomoles per gram of analysed tissue.

When Zimmer's team applied 30 micrograms of synthetic THC to the animals' ears it reduced the skin irritation by half. For comparison, a cannabis cigarette contains as much as 150 milligrams of THC.

Endocannabinoids may be produced by the body to dampen the immune response and so prevent allergic reactions, Zimmer believes. He also found that mouse skin cells exposed to synthetic THC release fewer cytokines, chemicals that attract immune cells to the site of infection or irritation.

Lowered attraction

Ramesh Ganju at the Harvard Cancer Center in Boston, Massachusetts, US, believes that a study he published in 2006 could also help explain what the European researchers found.

He revealed that dunking T cells - immune cells that flag foreign particles in the body and trigger allergy - into a solution containing synthetic THC caused them to become up to 70% less attracted to cytokine signals (Molecular Immunology, DOI:10.1016/j.molimm.2006.01.005).

Ganju says that Zimmer's findings provide further evidence that endocannabinoids "probably have a role in autoimmune diseases".

Zimmer agrees, suggesting that people with inflammatory conditions such as asthma and eczema might not produce enough endocannabinoids or related cell receptors. He adds that one day therapies based on THC-like compounds might be used to treat such disorders.

Researchers stress that people who currently suffer from autoimmune disease should not try to self-medicate with marijuana because of its side-effects.