About a decade ago, patients started coming to Dr. Alexander Pastuszak with a question that has only become more common since then: Would smoking weed make it more difficult for them to have children?
Dr. Pastuszak, an expert in male fertility but not a cannabis user, knew that laws and norms around marijuana were being relaxed across the country, and that many men were comfortable discussing their drug use with their physicians. He just didn’t have anything concrete to tell them.
“Until recently, the answer was, ‘I don’t know,’ ” said Dr. Pastuszak, who is now a urologist at the University of Utah.
So he started looking for an answer. Cannabis is legal for either medicinal or recreational purposes in all but 11 states and was used at least once by 52.5 million Americans in 2021, according to the Centers for Disease Control and Prevention. Yet because it remains illegal under federal law, it’s hard to study, and its long term health effects are still poorly understood, said Dr. Omer Raheem, a urologist at the Cleveland Clinic who practices in the United States and Abu Dhabi.
Even so, when it comes to the male reproductive system, some effects of cannabis are becoming clear. By looking at 48 studies from around the world, Dr. Pastuszak found in 2019 that cannabis products do harm a man’s chances of conceiving children. Finally, he feels, he has an answer for his patients.
“THC, certainly in smoked form, can impact semen,” Dr. Pastuszak said, and therefore damage male fertility.
Here’s what the experts have discovered.
How THC affects sperm cells
Experts have long known that tobacco and alcohol use can impact male fertility. And since at least the 1970s, researchers have suspected that cannabis use has a similar effect. But only recently have they been able to describe how it affects sperm cells, bending their shape, slowing them down and changing their genetic material.
It’s not surprising, since many cannabinoids are toxic to living cells, said Gerald M. Berkowitz, a cannabis expert at the University of Connecticut. “If you take plant or animal cells and you put them on a cell culture plate, and you put THC on that plate, you’ll see the cells die around THC.”
In studies conducted throughout the 1990s scientists at the University at Buffalo found that a cannabinoid in the body, called anandamide, plays a critical role in reproduction, preventing more than one sperm cell from fertilizing an egg at the same time. The same receptors used by anandamide could be hijacked by the THC in marijuana, the said, possibly overloading the sperm’s signaling system.
More recently, experts have investigated how this plays out in the real world. For instance, in his 2019 review, Dr. Pastuszak and several colleagues reported that cannabis use was strongly associated with lower sperm counts and concentration, as well as a higher incidence of abnormally shaped sperm.
The following year, a study of 229 Jamaican men showed that even moderate cannabis use was associated with a nearly three and a half times greater likelihood of misshapen sperm, which lowers the odds for a successful fertilization.
In addition, a new study of 113 Jordanian men found that sperm movement, called motility, was far lower in cannabis users than among tobacco smokers and nonsmokers, said Dr. Mohamed Eid Hammadeh, whose lab at Saarland University in Germany conducted the study. After THC bound to the sperm’s cannabinoid receptors, they found, it proceeded to damage the mitochondria inside the cell.
Known as the cell’s engine, the mitochondria propels the sperm toward the egg, explained Dr. Houda Amor, a co-author of the study with Dr. Hammadeh. With the mitochondria hobbled, the sperm struggles to swim.
Lastly, animal research suggests that cannabis may affect the DNA inside a sperm cell that contributes to the new embryo. A 2020 study with rats by Duke scientists found that paternal cannabis use harmed an offspring’s brain development.
How to mitigate the risk
Of course, cannabis can also affect male sexual health in ways that have nothing to do with sperm.
“Chronic high-dose use may contribute to erectile dysfunction, delayed ejaculation and diminished long-term sexual desire,” said Dr. Ryan S. Sultan, a clinical psychiatrist at Columbia. He cautioned that even smoking just once a week could trigger some of these effects.
Men should quit all cannabis use for at least three months before they want to start to get pregnant, said Ryan Vandrey, who researches cannabis use at Johns Hopkins University.
However, “there are lots of men of reproductive age who are heavy, heavy cannabis users and are having babies,” he added. “So it’s not that you can’t have a child if you’re a heavy daily cannabis user.”
Dr. Sultan recommended switching to edibles or vape products. But even though these other methods of using cannabis may have fewer harmful byproducts, they still deliver THC to the body.
If you’re concerned, seek out a fertility specialist, and of course eat a healthy diet nutrition and exercise regularly, both of which improve fertility. But there are no surefire ways to prevent any damage caused by THC.
“It’s better to quit smoking completely,” Dr. Hammadeh said.
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