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Cannabis Abstinence in Monkeys Reverses Harms of THC On Fertility, Study Finds

By Alexander Beadle

Published: Apr 12, 2023   
Macaque monkey sitting on a piece of wood.

Image credit: iStock

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In a study published last year, researchers from the Oregon Health & Science University (OHSU) found that chronic cannabis use could shrink the testicles of monkeys and cause problems with male fertility. However, it was not known whether these effects were permanent.

In a new study, published in the journal Fertility and Sterility, the researchers have confirmed that these effects are somewhat reversible after several months of abstinence.

Given the similarities in reproductive function between humans and the monkeys examined in this latest animal study, the researchers believe that these results could help inform the counseling that healthcare providers give to their patients.

Physical and hormonal effects of THC partially reverse with abstinence

In this new study, a group of six adult male rhesus macaque monkeys were given a THC edible once per day over the course of seven months, with the strength of the edible slowly increasing from a low dose to a high dose as the primates adjusted.

Over these months, the researchers observed that THC exposure led to a significant reduction in the size of the testes, as well as a negative impact on several male hormones that are linked to fertility. The researchers also found that the THC had impacted the sperm itself, altering the regulation of certain genes that are important for nervous system development in offspring, including genes that have been linked to autism spectrum disorder.

Following this exposure period, the monkeys were abstinent from cannabis for 140 days, during which the researchers continued to monitor any changes to the subjects’ reproductive health organs and testes, as well as the quantity and quality of their sperm.

By the end of this abstinence period, the researchers found that a number of the adverse reproductive health effects had been partially reversed. While testicular volume reduced by 59% during THC use, the testes recovered to 73% of their original volume following abstinence. Analysis of seminal fluid also showed that, of the 80 proteins whose expression had been affected by the THC, 60 were fully restored by the study end.

However, there were some important proteins that were not restored after stopping use of the THC edibles. For example, levels of heat shock protein A5 did not seem to recover after abstinence. Heat shock proteins have previously been seen to be decreased in individuals with reduced sperm motility, which is an important factor in male infertility.

Providing better information to patients

Based on their findings, and the close similarity of these nonhuman primates to humans, the researchers say that the results of their study could build the groundwork for clinicians looking to give more informed advice to their patients seeking guidance around cannabis use and/or fertility issues.

“We understand that for teens and young adults, family planning might not be top of mind; however, THC even in moderate doses could impact their fertility outcomes, so this is a serious concern for us as healthcare providers,” lead study author Jason C. Hedges, an associate professor of urology in the OHSU School of Medicine, said in a statement.

“The more we can understand and define this issue, the better information we can provide to patients to be able to optimize their reproductive health.”

Moving forward, the OHSU research team will continue to research the impacts of THC use on reproductive health. In particular, the team hopes to conduct similar studies examining the effects of chronic THC use through different modes of consumption, such as smoking or vaping. The team also wishes to conduct additional research looking at the effects of THC use on fetal and offspring development.

“It’s so important that we research, understand and educate about the implications of THC on reproductive health, especially as use continues to increase among individuals of reproductive age and more states legalize cannabis,” study author Jamie Lo, an associate professor of obstetrics and gynecology at the OHSU School of Medicine, said in a statement. Lo is also an adjunct associate professor of urology at the Oregon National Primate Research Center (ONPRC).

“These findings are important because we can now more confidently assure patients that by abstaining from THC for at least four months, the impacts of THC on male fertility can be partly reversed,” Lo said. “This allows for more concrete, informed recommendations for patients who are in the process of family planning or actively trying to conceive.”

Cannabis and fertility

While more research into cannabis and its effects on the reproductive system is still needed, the current body of research generally points towards THC adversely affecting fertility.

Writing in the Canadian Medical Association Journal, researchers at Western University in London, Ontario, summarized a brief “five things to know” about cannabis and fertility. This included a description of how THC can act on endocannabinoid receptors present in the internal reproductive organs, as well as references to studies suggesting that cannabis could delay ovulation in females and reduce sperm count in males.

Other researchers have found that exposure to THC may reduce the likelihood of eggs resulting in a viable pregnancy. One rat study also determined that not only did THC reduce sperm count and sperm motility in mice directly exposed to the THC, but it also had a negative effect on the sperm of their offspring.

Interestingly, in one recent study from researchers at Landmark University, Nigeria, ethanolic leaf extract of cannabis (ELEC) actually improved the sperm and testicular health of mice. The researchers believe that this may be down to the antioxidant properties of the flavonoids present in ELEC, which could be protecting the reproductive system from damage via oxidative stress.


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