Researchers discovered that two cannabinoids, the active chemicals found in the drug, prevent cancer cells from multiplying and in some instances actually kill the cells.

But cancer experts warned people suffering from prostate cancer not to treat themselves by smoking cannabis as more work is needed to explore ways in which the chemicals could be used to benefit patients.

Dr Lesley Walker, Cancer Research UK’s director of cancer information, said: “This is interesting research which opens a new avenue to explore potential drug targets but it is at a very early stage – it absolutely isn’t the case that men might be able to fight prostate cancer by smoking cannabis.

“This research suggest that prostate cancer cells might stop growing if they are treated with chemicals found in cannabis but more work needs to be done to explore the potential of the cannabinoids in treatment.”

Prostate cancer is the second most common form of the disease among men in Scotland and about 2500 new cases are diagnosed every year. A total of 793 men died from prostate cancer in 2007 and official figures show that 19.9% of patients with the disease will have died within five years of diagnosis.

Researchers from the University of Alcala in Madrid used artificial molecules that are similar to two cannabinoids and tested their effect on prostate cancer cells grown in a lab. They also carried out tests on mice that had been transplanted with human prostate cells.

The researchers found that if the cannabinoids bind to a receptor called CB2, the cancer cells stop multiplying and in some instances die. When the CB2 receptor was switched off, the prostate cancer cells carried on dividing and growing.

Cancer Research UK said the study, published in the British Journal of Cancer, suggested that the CB2 receptor, one of two forms of cannabinoid receptors, plays a pivotal role in stopping the spread of prostate cancer cells.

The other receptor, CB1, is responsible for the psychoactive effects of cannabis so it is hoped that the new discovery will allow scientists to concentrate on the development of drugs targeting the CB2 receptor, which would enable prostate cancer to be treated without causing the same side-effects.

Professor Ines Diaz-­Laviada, study author at the University of Alcala, said: “Our research shows that there are areas on prostate cancer cells which can recognise and talk to chemicals found in cannabis called cannabinoids.

“These chemicals can stop the division and growth of prostate cancer cells and could become a target for new research into potential drugs to treat prostate cancer.”

The potential medicinal benefits of cannabis, which is a Class B drug, were recognised in the nineteenth century and Queen Victoria was rumoured to use the drug to treat menstrual pains.

Since then, research has been ongoing to discover new ways to use the drug to treat a range of conditions.