A recent study was conducted by scientists at Harvard Medical School’s Center for Infertility and Reproductive Surgery and published several weeks ago in Reproductive Physiology and Disease.
The study looked at semen samples from 12 “healthy” males who reported that they were “chronic and heavy users of inhaled cannabis.” All participants indicated they had used the drug between 25 and 30 days of the last month, and most said they had been regular consumers for at least five years. Men of reproductive age, the study’s authors note, “are the most prevalent consumers of marijuana, with 19.4% of men in the USA reporting use.” A 2018 study cited by the authors found that 16.5 percent of men and 11.5 percent of women reported using marijuana while attempting to conceive.
The study didn’t just look at THC and the primary THC metabolite, 11-OH-THC, in semen samples. It also assessed THC and metabolite levels in the subjects’ blood and urine. All urine samples contained detectable amounts of THC and 11-OH-THC, which confirmed that the subjects had consumed cannabis.
Only two of the semen samples contained THC and metabolites above the reporting level of 0.5 ng/mL: at “0.97 nanograms per milliliter and 0.87 ng/mL.”
If those ng/mL values look like a foreign language to you, they indicate that only incredibly tiny amounts of THC will pass the blood-testis barrier, a membrane that keeps contaminants in the bloodstream from damaging the little fellas swimming around inside of the testicles.
But it wasn’t clear what set those two participants apart. There was no correlation between semen THC and concentration of the metabolite THC carboxylic acid in urine, nor with time since last cannabis consumption, participant age or participant body mass index.
“It is puzzling that some, but not all, semen samples tested positive for THC,” the study says. “There were no obvious factors that were strongly associated with detectable semen THC; thus, we can propose few predictors of the presence of THC in human semen. Future directions (of research) include identifying characteristics that may affect semen detectable THC levels.”
The primary goal of the proof-of-concept research, they explain, “was to determine whether THC can cross the blood-testis barrier.” On that front, they appear to have succeeded.
“In the setting of a growing repository of data surrounding the effects of the endocannabinoid system in the regulation and maintenance of fertility and early pregnancy,” the study says, “ours is the first report that the exogenous cannabinoid THC can be detected in any human reproductive matrix.”
“Our findings, that THC can be directly quantified in human seminal fluid, lay the groundwork to allow for future studies,” the new study says. “Since THC can be detected in the seminal fluid of some individuals, this might provide a direct method of measurement (rather than relying on self-reporting marijuana use, which is subjective and potentially unreliable, or serum levels which only reflect recent exposure) to bridge real-world clinical studies with the prior staged studies in which THC was directly incubated with washed sperm.”
How THC affects sperm, conception, pregnancy or childhood development, is still hard to say. There has been several conflicting studies on marijuana-induced infertility in men. Some studies have found that men who smoke marijuana have a higher sperm count. Other research has found they have a lower sperm count. In other words, moderation is best in this case too.
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