Reproduction is one of the less-publicised places the endocannabinoid system operates, and it turns out to be involved at several steps: sperm function and their journey through the reproductive tract, ovulation, and embryo implantation.
The evidence in humans is limited. It leans in one direction, which is enough to inform a decision without justifying alarm.
Male Reproductive Effects
Sperm parameters. Studies have reported associations between cannabis use and reduced sperm concentration and total sperm count, along with changes in morphology in some research. Findings are not uniform, and at least one study reported the opposite direction for concentration, which is a genuine inconsistency rather than something to hide.
Sperm motility and function. CB1 receptors are present on sperm, and endocannabinoid signalling appears involved in motility and in the capacitation process sperm undergo before they can fertilise an egg. Excessive cannabinoid signalling may interfere with the timing of that process, which is a plausible mechanism for reduced fertility that does not require reduced sperm counts.
Hormones. Effects on testosterone are inconsistent across studies. Some report reductions with heavy use, others no significant change. This is not a settled finding.
Reversibility. Spermatogenesis takes roughly 70 to 90 days, so effects on sperm production are potentially reversible over a cycle of about three months after stopping. That figure is useful for planning.
Female Reproductive Effects
Ovulation. Research has associated cannabis use with disrupted ovulation and menstrual cycle irregularity, and THC can affect the hormonal signalling that drives the cycle, including luteinising hormone.
Time to conception. Some studies report longer time to pregnancy among people who use cannabis, with heavier use associated with greater delay.
Implantation. Anandamide signalling appears to be involved in embryo implantation timing, and the window for implantation is narrow. Disrupted signalling is a plausible mechanism for reduced success, established mainly in animal work.
Pregnancy Is a Separate and Clearer Question
Once pregnant, the picture is not ambiguous. Cannabis crosses the placenta, prenatal exposure is consistently associated with lower birth weight, and studies report associations with attention, behavioural and cognitive differences in childhood. The endocannabinoid system is involved in neurodevelopment. Major obstetric bodies advise against use in pregnancy.
THC also passes into breast milk and has been detected there for days after use, with reports up to around six days, so avoidance during breastfeeding is advised.
Fertility Treatment
If you are undergoing IVF or other assisted reproduction, this becomes more concrete. Some research has reported associations between cannabis use and poorer outcomes in assisted reproduction, including effects on oocyte retrieval numbers.
Fertility treatment is expensive, emotionally demanding and time limited. Stopping cannabis for the duration is a low-cost decision against an uncertain but plausible risk, which is a straightforward calculation even without conclusive evidence.
What the Evidence Does Not Show
Being honest about the limits matters here, because fertility anxiety is easily exploited.
The reasonable framing is that cannabis is one modifiable factor among several, not a primary cause of infertility.
Practical Guidance
Bottom Line
Endocannabinoid signalling is involved in sperm capacitation, ovulation and implantation, and human studies associate cannabis use with reduced sperm parameters, disrupted ovulation and longer time to conception. The evidence is observational and modest, and none of it supports permanent infertility. Stopping while trying to conceive, during fertility treatment, in pregnancy and while breastfeeding is the sensible position.
Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before making any health-related decisions.