The active compound in marijuana, THC, can slow the growth of lung tumours and reduce the spread of the cancer in mice, a preliminary study reveals.

Human lung cancer tumours grew less than half as fast in mice that received moderate doses of the compound, the researchers reveal. They hope that drugs mimicking the apparent anti-cancer effects of tetrahydrocanabinol (THC) could one day help treat patients. The team strongly discourage people from self-medicating by smoking marijuana, noting that doing so could potentially encourage tumour growth.

Ramesh Ganju at the Harvard Cancer Center in Boston, Massachusetts, US, and colleagues deposited human lung cancer cells under the skin of a dozen mice and allowed the tumours to grow in the animals for about two weeks. They then began giving half of these mice daily injections of about 250 micrograms of synthetic THC right next to the tumours for three weeks. A marijuana cigarette may contain as much as 150 milligrams of THC.

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Cannabis extracts may shrink brain tumours and other cancers by blocking the growth of the blood vessels which feed them, suggests a new study.

An active component of the street drug has previously been shown to improve brain tumours in rats. But now Manuel Guzman at Complutense University, Spain, and colleagues have demonstrated how the cannabis extracts block a key chemical needed for tumours to sprout blood vessels – a process called angiogenesis.

And for the first time, the team has shown the cannabinoids impede this chemical in people with the most aggressive form of brain cancer - glioblastoma multiforme.

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How come you can get different highs from different strains of marijuana? Don't they just all contain THC?

Marijuana has two powerful active ingredient - THC and CBD (cannabidiol). Both substances are cannabinoids which produce psychoactive effects by binding with special receptors which are extraordinarily abundant all over the brain and body. Your brain makes it own cannabinoid - anandamide - which is thought to be involved in pain sensations, memory regulation and the immune system.

The relatives amounts of these two ingredients (THC and cannabidiol) plus small input from over sixty different cannabinoids in the plant determine the subtle differences in types of high you can get from different strains of the cannabis plant.