31st March 2004

Men who smoke cannabis could be affecting their fertility, according to new research presented today1.

Researchers2 at Queen’s University, Belfast, have discovered that THC – the active ingredient in cannabis – impedes sperm motility and impairs its ability to penetrate the egg for fertilisation.

During a multi-centre study on the lifestyle habits of infertile men, researchers noticed that many men attending for infertility investigations at the Royal Maternity Hospital were using cannabis on a regular basis. This led them to commence a study looking at the direct effects of THC.

The study by the Reproductive Medicine Research Group discovered that THC impedes sperm motility making it less likely that the sperm will reach the egg to fertilise it. And that another key function of the sperm – to digest the egg’s protective coat with enzymes in a bid to aid sperm penetration – is impaired in the presence of cannabis.

Fifty-one semen samples were used, split, and treated with THC or simply incubated as a control. THC-treated samples were found to be up to 45% less forward moving and up to 30% of THC-treated sperm don’t release the enzymes needed to penetrate the egg.

Dr Sheena Lewis, from the Department of Obstetrics and Gynaecology, who leads the Reproductive Medicine Research Group, said recent reports carried out on sea urchin sperm suggest that cannabis may be a major cause of infertility by inhibiting sperm functions necessary for fertilisation.

These experiments on human sperm tell the same story,’ she said.

Speaking at the annual British Fertility Society annual meeting on 31 March, Dr Lewis said: ‘Following the Government’s recent reclassification of cannabis from Class B to Class C the need to determine its effects on male fertility is even greater so that men can make an informed choice about smoking the drug if it is a health risk.’

‘Infertility already affects one in six couples across the United Kingdom and 40 per cent of these cases are due to problems with sperm.’

Dr Lyn Whann, who presents some of the work today, added ‘It is estimated that 3.2 million people in Britain smoke cannabis and that figure may now increase. Add the two together and we may find that the use of recreational drugs will exacerbate male fertility problems.

Notes for Editors

1The effects of Tetrahydrocannabinol (THC), the primary psychoactive cannabinoid in marijuana, on in vitro human sperm motility is presented at The Annual British Fertility Society Meeting 2004 on Wednesday 31st March 2004, in Cheltenham, UK
2LB Whann*, N McClure*# and SEM Lewis* from *School of Medicine, Obs and Gynae, Queen’s University, Belfast and #Regional Fertility Centre, Royal Maternity Hospital, Belfast, Northern Ireland, UK