Cannabis danger to men

Men are today warned that smoking cannabis could affect their fertility. Scientists have uncovered new evidence that the drug upsets the male reproductive system.

They fear it could reduce the amount of testosterone - which plays a key role in sperm production - produced by the body.

It may have a serious impact on the body's natural hormones and they want more research to assess the risk.

The warning comes in a study by scientists at Aberdeen University, who examined the impact of cannabis on male mice.

The animals, whose reproductive systems are similar to those of humans, were injected with cannabinoids - cannabis derivatives - to see if they changed natural messages from the brain to the testes regulating testosterone production.

Because the testes also produce testosterone of their own accord, as well as reacting to brain signals, the research team also looked at whether cannabis affected this function.

The results suggest that the drug has a significant impact on both processes.

Dr Paul Fowler - from the university's department of obstetrics and gynaecology - who led the research, said: "Our study suggests that cannabis interferes with the hormones needed for reproduction.

"It appears to affect the way the testes make and release testosterone, and has an impact on the way the brain regulates production of the hormone."

The team found that in mice, cannabis may actually boost the amount of testosterone produced as a result of brain signals, but it reduces the amount produced by the testes. Dr Fowler said: "These two things could add together to have a serious negative impact on testosterone production."

The research, to be unveiled at a major fertility conference in Aberdeen today, reignites the debate about the potential dangers of so-called soft drugs.

Cannabis is the most widely used drug in the United Kingdom after alcohol and cigarettes. Home Office figures suggest that a third of all 15-year-olds have tried it. Experts estimate it is responsible for 30,000 deaths in the UK every year. Last month, it emerged that cannabis users are seven times more likely to suffer from mental illness, triggering fears of an epidemic of schizophrenia.

The United Nations drugs watchdog has warned that the Government's "softly, softly" approach is putting the health of a generation at risk. Critics say the decision to downgrade it to a Class C drug has sent out the wrong message, encouraging people to think it is safe. Studies show that nine out of 10 children believe it is legal.

Scientists have speculated that falling sperm counts among European men are due to the surge in the use of recreational drugs. Previous studies on mice suggest that women who smoke marijuana during pregnancy risk damaging their baby's reproductive system.