About a decade ago, patients began approaching Dr. Alexander Pastuszak with a pressing question: does smoking weed affect their fertility?
As an expert in male fertility but not a cannabis user, Pastuszak recognized a shift in societal attitudes toward marijuana.
With laws and norms increasingly relaxing across the United States, many men felt comfortable discussing their drug use with their physicians.
Yet despite the growing concerns, Pastuszak realized he didn’t have concrete answers to provide these patients.
“Until recently, the answer was, ‘I don’t know,’” he remarked.
Motivated to find an answer, Pastuszak began researching the effects of cannabis on male fertility.
Cannabis is now legal for either medicinal or recreational purposes in all but 11 states, with reports indicating that at least 52.5 million Americans used it at least once in 2021, according to the Centers for Disease Control and Prevention.
However, its classification as illegal under federal law poses problems for researchers, leaving many long-term health effects poorly understood, according to Dr. Omer Raheem, a urologist at the Cleveland Clinic.
Despite these challenges, findings regarding cannabis’s impact on male reproductive health are becoming clearer.
Pastuszak conducted a comprehensive review of 48 studies worldwide in 2019, revealing that cannabis usage could significantly harm a man’s chances of conceiving children.
“THC, certainly in smoked form, can impact semen and therefore damage male fertility,” Dr. Pastuszak stated.
But how exactly does THC affect sperm cells?
Experts have long been aware that substances like tobacco and alcohol can adversely influence male fertility.
Cannabis had been suspected of having a similar effect since at least the 1970s.
Recent studies have detailed how cannabis impacts sperm cells by changing their shape, slowing them down, and altering their genetic material.
Gerald Berkowitz, a cannabis expert at the University of Connecticut, notes that many cannabinoids can be toxic to living cells.
“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,” he explained.
Research from the 1990s at the University at Buffalo also highlighted how the body’s natural cannabinoid, anandamide, plays a crucial role in reproduction.
Anandamide prevents multiple sperm cells from fertilizing an egg simultaneously, but THC could disrupt this process by overwhelming the sperm’s signaling system.
In his 2019 review, Pastuszak noted a strong association between cannabis use and lower sperm counts, concentration, and increased occurrence of abnormally shaped sperm.
In a follow-up study conducted the next year with 229 Jamaican men, researchers found that even moderate cannabis intake correlated with a nearly 3.5 times higher likelihood of misshapen sperm, which adversely affects successful fertilization.
Another study involving 113 Jordanian men revealed that sperm movement—or motility—was significantly lower among cannabis users compared to tobacco smokers and nonsmokers.
Dr. Mohamed Eid Hammadeh, whose lab at Saarland University in Germany conducted the study, explained that when THC binds to the sperm’s cannabinoid receptors, it damages the mitochondria within the cells.
Known as the cell’s engine, mitochondria help propel the sperm toward the egg.
With impaired mitochondria, sperm struggles to swim effectively.
Animal studies have further indicated that cannabis use might also impact the DNA within the sperm, which is crucial for early embryo development.
A 2020 study conducted by Duke scientists on rats discovered that paternal cannabis use could negatively affect offspring brain development.
To mitigate these risks, experts recommend that men refrain from all cannabis use for at least three months prior to trying to conceive.
Ryan Vandrey, a researcher at Johns Hopkins University, emphasized this timeframe for quitting.
Despite this, he noted, “There are lots of men of reproductive age who are heavy, heavy cannabis users and are having babies.”
Dr. Ryan S. Sultan, a clinical psychiatrist at Columbia University, also pointed out that chronic high-dose cannabis use could contribute to erectile dysfunction, delayed ejaculation, and diminished long-term sexual desire.
He cautioned that even smoking just once a week could trigger some negative effects.
While some experts suggest switching to edibles or vape forms of cannabis, they maintain it is still delivering THC to the body.
For men concerned about their fertility, seeking the guidance of a fertility specialist is wise.
In addition to quitting cannabis, experts recommend focusing on a healthy diet and regular exercise, both of which can enhance fertility.
However, there are no guaranteed methods to prevent damage caused by THC.
“It’s better to quit smoking completely,” Hammadeh concluded.
image source from：https://www.sltrib.com/news/nation-world/2025/04/13/your-weed-habit-may-be-messing/
