Overview

This study found that chronic THC use alters the sperm epigenome in genes involved in nervous system development and autism spectrum disorder, which may impact long-term offspring outcomes. Discontinuation of THC for at least 4 months resulted in partial reversal of these changes.

Study Need and Importance

Cannabis is the most commonly used psychoactive drug among reproductive-age males in the United States and worldwide.¹ This high prevalence continues to rise and is extremely concerning as safety data are substantially lacking. Cannabis users are often unaware of the potential adverse impacts on their fertility, in part because health care providers lack evidence-based knowledge regarding the effects of cannabis use and are unable to advise patients. Currently, the American Society for Reproductive Medicine discourages the use of cannabis in patients intending to conceive because the full impact on reproductive health has not been clearly established.²

Published studies examining the effect of cannabis exposure on male fertility and future offspring are conflicting. The existing human literature is limited in part due to confounders including polysubstance use, small sample sizes, retrospective and observation study designs, self-report, and an inability to determine the dose, frequency, and timing of cannabis use.³ Animal studies have largely focused on the effects of acute THC exposure, which was often delivered via intraperitoneal injection or oral gavage, not representative of typical human use.^4,5

To overcome the limitations of prior studies, our group used a translational rhesus macaque model which allows for standardization of subject variability, δ-9-tetrahydrocannabinol (THC, the main psychoactive component of cannabis) exposure, and experimental manipulation to elucidate direct biological consequences of chronic cannabis use while controlling for potential confounders. Using our rhesus macaque model of chronic THC edible consumption, our group had previously uncovered a highly concerning series of deleterious effects of chronic cannabis exposure on male fertility, including significant reduction in testicular volume and impacted male reproductive hormones.⁶

Building upon our prior work, the objective of this study was to determine the effect of chronic THC use on the sperm epigenome and whether these changes are permanent or temporary with discontinuation of THC in our rhesus macaque model. Rhesus macaque males were administered a daily THC edible over ∼7 months (∼4 spermatogenesis cycles) with serial semen collections. Whole genome bisulfite sequencing was performed on DNA extracted from collected sperm at baseline (before THC exposure), following chronic exposure to THC (2.5 mg/7 kg/d, equivalent of a human heavy medical cannabis dose), and after THC discontinuation for ∼4 months (∼2 spermatogenesis cycles).

What We Found

Our study demonstrated that chronic THC exposure altered sperm DNA methylation of genes involved in nervous system development and autism spectrum disorder that may impact long-term offspring outcomes (see Figure). There was significant overlap of affected genes between rhesus macaques and published gene lists of human cannabis users. Cessation of THC use over a period of 4 months partially restored adverse impacts to male reproductive health and THC-associated changes to sperm DNA methylation in genes important for development (see Figure). Nonrestored changes in sperm DNA methylation were enriched for genes involved in nervous system development and function, synaptogenesis signaling pathway, and sperm motility.

Figure. Chronic THC use impacts the sperm epigenome and alters genes in rhesus macaques related to nervous system development and function, and autism spectrum disorder that may impact long-term offspring outcomes. These changes were partially restored with discontinuation of THC. FSH indicates follicle-stimulating hormone.

Limitations

A limitation of the nonhuman primate model is the smaller animal cohort size, which was addressed in our study by using a single-case longitudinal experimental design in which each male served as its own control during the study to minimize inter-animal variability. In addition, our study performed nonsedated collaborative semen sample collections early in the morning to try to avoid self-ejaculation prior, but it is possible that we were not always successful in doing so, and that can impact the semen parameter and sperm count in the collected sample.

Interpretation for Patient Care

This is the first study to establish the benefit of cannabis cessation on male fertility and insight to the minimum duration of abstinence from THC in rhesus macaques. These data can be translated directly to the clinical setting to guide health care providers in counseling male patients about how far in advance (minimum 4 months) they should discontinue THC use prior to trying to conceive. Future studies from our group will focus on the effects of chronic THC use over long periods of time and through various modes, such as vaping, as well as investigating the impacts of THC on fetal and offspring development.