Having Trouble Conceiving? Stop Smoking Pot

By Shawn Dwyer 06/05/14

A new study into male fertility revealed that size and shape really do matter.


While it’s hardly news marijuana has an effect on male sperm count, a new study has shown that the reason pot smokers have trouble impregnating their significant other is that weed affects the size and shape of a man’s sperm.

Conducted by researchers at the University of Sheffield in South Yorkshire, England, the study was published in the journal Human Reproduction and collected semen samples from 1,970 men from 14 fertility clinics across England. Researchers initially wanted to focus on how a man’s lifestyle affected the size and shape of his sperm without focusing specifically on cannabis, but were unable to ignore the results in their conclusion.

"We weren't really interested in [marijuana] at all," said lead researcher Dr. Alan Pacey, senior lecturer in andrology at the University of Sheffield.  "We were interested in trying to best define the risks of sperm quality...It was just one of the things we asked if they did; it was no more detailed than that."

Of the 1,970 men who were studied, researchers found that 318 produced abnormal sperm, where less than four percent were the correct size and shape. The other 1,600 men had a higher percentage of so-called normal sperm.

"Cannabis smoking was more common in those men who had sperm morphology less than four percent," said Pacey. "Cannabis affects one of the processes involved in determining size and shape. And we also know that the way cannabis is metabolized is different in fertile and infertile men."

The Sheffield study was able to add to the growing amount of evidence that shows marijuana’s effect on male fertility, though according to Rebecca Sokol, president of the American Society for Reproductive Medicine, the results were hardly conclusive.

"The take-home lesson of the article is that clinicians should counsel their patients on the possible relationships between lifestyle factors, abnormal semen parameters and fertility outcomes," Sokol said. "This should include a discussion that the data are often inconclusive, but the motto 'everything in moderation' is a wise approach for the couple who is planning a pregnancy."

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Shawn Dwyer is a writer, editor and content producer living in Los Angeles. You can find him on Linkedin.