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Cannabis Edibles Shrink the Testicles of Monkeys, Study Finds

By Leo Bear-McGuinness

Published: Feb 01, 2022   
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THC can reduce the size of monkey testicles, according to a new paper.

Published in Fertility and Sterility, the study involved six macaque monkeys that were fed THC-laced edibles for seven months. By the end of the study, the monkeys’ testicles had more than halved in size.

Given the rise of cannabis legalization across North America, the authors of the paper say that their findings may have implications for the fertility of human cannabis consumers.

Monkey business

To begin their study, the researchers from Oregon Health & Science University first acquired six adult macaques, all of which had proven paternity. The animals were fed one THC-laced cookie daily, in addition to their standard diet.

To study the impact of low, moderate, and high THC doses, the THC content of the cookies – which were supplied by the National Institute of Drug Administration – increased every 70 days; the macaques were first fed 0.5 milligrams (mg) per 7 kilograms (kg) per day, then 1 mg/7 kg/day, then 2.5 mg/7 kg/day.

After seven months of eating the edibles, all six of the macaques had smaller testicles – 58 percent smaller, on average. The reduction of the gonads seemed to be linked to the increasing THC doses, as the macaques’ testicles continued to decrease, on average, over the course of the seven months.

How could THC have caused this testicular truncation? Well, the researchers aren’t exactly sure, but they do write that the cannabis compound likely acted on the cannabinoid receptors found throughout the male reproductive tract.

But altered hormone levels may also have played a role. The researchers observed that, in addition to shortening the macaques’ testicles, their THC diet also seemed to increase their levels of the sex hormones LH and FSH and reduce their levels of testosterone.

To properly determine the cause of the macaques’ diminished gonads, however, further anatomic studies on THC-exposed testicular tissue will be needed, say the researchers.

Aside from the size of the macaques’ testicles and their hormone levels, the research team observed no significant changes in the monkeys’ sperm numbers, sperm morphology, or sperm motility. All macaques put on a little weight over the course of the study (likely due to their daily cookies), but their general behavior remained unchanged.

While the research team acknowledge their study’s limitations – it studied only six subjects, none of them human, etc. – they maintain that their findings indicate that chronic THC exposure can lead to a significant dose-dependent depletion of testes. Furthermore, they say their results could be used to inform fertility services for cannabis consumers.

“Because marijuana use is becoming more common, with significantly increased potency, our study provides important insight regarding the potential consequences of marijuana use that would help providers guide couples who are interested in conception or are affected by male infertility,” they write in their paper.

Sativa and sperm

The macaque study may be “the first study using a NHP [nonhuman primate] model to examine the impact of chronic THC use on male reproductive health,” but it’s far from the first study to examine how cannabis impacts male fertility.

A recent study from researchers at Washington State University found that, when exposed to vaporized cannabis flower three times a day for ten days, mice had lower levels of sperm and sperm motility. More concerningly, the researchers found that these defects were also found in the next generation of direct male offspring.

“This is a warning flag,” study author Dr Kanako Hayashi, said in a statement at the time. “You may take cannabis for some kind of momentary stress, but it could affect your offspring.”

On the other hand, some studies have found evidence that cannabis may actually increase sperm counts.

Published in 2019, one study conducted by a team at the Harvard T.H. Chan School of Public Health found that men who reported smoking cannabis at some point in their life had higher sperm concentrations and higher levels of testosterone than those who had never used cannabis. But as high testosterone levels are also linked with risk-seeking behaviors, such as illicit cannabis use, this link may have been indirect.  


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