Cannabis lowers fertility by shrinking sperm

Smoking cannabis can reduce a man’s fertility by altering the size and shape of his sperm and, more surprisingly, sex in the summer months has a similar effect, scientists found.

Conversely, abstaining from sexual activity for more than six days improved the “morphology” of sperm.

There was also reassuring news for prospective fathers who might be considering drastic lifestyle changes. Common lifestyle factors, including smoking cigarettes and drinking alcohol, had little effect on sperm quality.