Marijuana, or cannabis, is derived from the Cannabis sativa or Cannabis indica plant and contains hundreds of compounds known as cannabinoids. The two most studied are delta-9-tetrahydrocannabinol (THC), the primary psychoactive component, and cannabidiol (CBD). As global use increases, a central question is how these compounds affect the ability of men and women to conceive. Scientific understanding suggests that marijuana compounds interact with the body’s existing biological system, potentially disrupting reproductive health and fertility.
How Cannabinoids Interact with Reproductive Systems
The influence of external cannabinoids, like THC and CBD, stems from their ability to interact with the body’s own regulatory network, the endocannabinoid system (ECS). The ECS is composed of naturally produced compounds (endocannabinoids), enzymes, and specialized receptors. This system is distributed throughout the body, including in reproductive tissues.
The two main receptors are Cannabinoid Receptor Type 1 (CB1) and Type 2 (CB2). CB1 receptors are concentrated in the central nervous system but are also found in the testes, ovaries, and uterus. CB2 receptors are associated with immune cells but are also present in reproductive organs. The presence of these receptors indicates the ECS naturally regulates reproductive processes.
When THC is consumed, it mimics natural endocannabinoids and binds to CB1 and CB2 receptors, altering the system’s balance. This interaction can disrupt the signaling cascades that control the development of sperm and eggs, hormone release, and the conditions necessary for a successful pregnancy. The impact of cannabis on fertility is based on interference with this fundamental biological communication network.
Effects on Male Reproductive Function
The most consistent evidence regarding cannabis use in men relates to its negative impact on semen parameters. Studies show that chronic or frequent marijuana use is associated with a reduction in both sperm count and concentration. For instance, men using marijuana more than once a week often have a significantly lower sperm concentration compared to non-users.
Cannabis compounds also directly impair the functional capacity of sperm cells. Use can lead to reduced sperm motility, which is the ability to move efficiently toward the egg. Furthermore, male users may show a higher rate of abnormal sperm morphology, meaning the sperm cells have unusual shapes that hinder function.
Sperm cells possess cannabinoid receptors, suggesting that THC can interfere with necessary steps for fertilization, such as capacitation. Capacitation is a maturation process sperm must undergo in the female reproductive tract to become capable of fertilization. Cannabinoid exposure may inhibit this preparation.
The influence of cannabis extends to the hormonal axis regulating male reproduction. Frequent use may lower levels of Luteinizing Hormone (LH), which stimulates testosterone production in the testes. The effect on Testosterone levels is variable, however, with some studies reporting a decrease and others showing an inconclusive response. Follicle-Stimulating Hormone (FSH), which drives sperm production, generally shows minimal change.
Effects on Female Reproductive Function
In women, cannabinoids interfere with the hormonal communication system known as the Hypothalamic-Pituitary-Ovarian (HPO) axis. This axis controls the release of key hormones, including Gonadotropin-Releasing Hormone (GnRH), which regulates the menstrual cycle. Exogenous cannabinoids, particularly THC, suppress the release of GnRH, disrupting the cyclical pattern of female hormones.
This hormonal disruption can manifest as irregularities in the menstrual cycle, including delayed or anovulatory cycles, where an egg is not released. This suppression of ovulation directly reduces a woman’s chance of conceiving. Studies in animal models, such as non-human primates, show that chronic THC exposure leads to ovulatory dysfunction and altered hormone levels.
The ECS also plays a role in processes occurring after fertilization. Cannabinoid receptors are present in the fallopian tubes, and THC exposure may alter the movement of the fertilized egg toward the uterus. The uterine lining (endometrium) also expresses these receptors, and the balance of endocannabinoids is necessary for successful embryo implantation.
An imbalance in the ECS within the uterus can impair the ability of a developing embryo to attach to the uterine wall. Laboratory studies indicate that THC exposure negatively affects the quality of the female egg (oocyte). This occurs by altering gene expression and increasing chromosomal errors, which lowers the likelihood of producing a viable embryo.
Contextualizing the Current Research
Drawing definitive conclusions about cannabis and human fertility is complicated by research limitations. Many studies rely on self-reported usage, which introduces bias due to varying honesty and recall accuracy. It is also difficult to accurately quantify the dose and potency of the cannabis consumed, given the high variability in modern products.
A confounding factor is that many marijuana users also consume other substances, such as tobacco or alcohol, making it challenging to isolate the effect of cannabis alone. Furthermore, ethical constraints prevent controlled clinical trials where human subjects are intentionally exposed to THC to study fertility outcomes.
Consequently, detailed mechanistic evidence often comes from laboratory settings or animal models, which may not perfectly translate to human physiology. Human studies are often observational or involve couples already seeking fertility treatment, potentially skewing results toward those facing reproductive challenges. Although some large population studies have not found a prolonged time to pregnancy, the biological evidence consistently points to potential mechanisms of harm.