Revealing how lifestyle affects fertility

Sperm illustration

Our research has shown that the size and shape of sperm is affected by cannabis use.

The findings are based on an investigation into lifestyle and sperm morphology - the size and shape of sperm.

The study, which looked at samples from almost 2,000 men, showed that cannabis negatively affected sperm morphology.

As many as 318 men of the 1,970 who were tested had sperm of which less than four per cent was normal. These men were also more than twice as likely to have smoked cannabis in the three months prior to their sample being taken.

It is reassuring to find that there are very few identifiable risks, although our data suggests that cannabis users might be advised to stop using the drug if they are planning to try and start a family.

Professor Allan Pacey, Academic Unit of Reproductive and Developmental Medicine

Sperm morphology is an important factor in fertility. In order for sperm to pass into the woman’s body following sex, it needs to be the correct size and shape.

However, while cannabis use was shown to have a negative impact on sperm morphology, the study also demonstrated that other lifestyle factors such as smoking, alcohol and type of underwear had little effect on sperm morphology.

Lead author Professor Allan Pacey from our Academic Unit of Reproductive and Developmental Medicine said: "It is reassuring to find that there are very few identifiable risks, although our data suggests that cannabis users might be advised to stop using the drug if they are planning to try and start a family."

"Men don’t have to live like a monk in order to conceive. Factors such as body mass index and alcohol consumption have little effect on sperm morphology. And while people shouldn’t smoke for other health reasons, it doesn't influence the size and shape of sperm."

But there were some lifestyle factors that affect sperm morphology, as Professor Pacey explains. "We also looked at occupational risks and the research does show that men who work with paint strippers and lead are at a greater risk of having poor sperm morphology."