There is a popular narrative circulating around the anti-cannabis lobby - that increasing legal access to marijuana, medical or otherwise, will lead to a crisis in male fertility with a sharp drop in testosterone and overcooled and rather directionless sperm.
However, if we turn to the available human data, any media hysteria over marijuana seems largely unwarranted. Instead, evidence suggests that regular marijuana consumption can affect testosterone levels. Some studies suggest that regular marijuana use lowers testosterone levels, while other studies, on the contrary, correlate marijuana use with increased testosterone levels. The significance of the relationship between marijuana and testosterone levels is not yet fully understood.
CBD oil and testosterone
Before we get into most of what we know about cannabis and testosterone, it's important to be clear that we're going to be talking mainly about THC, because very little research has been done on the subject of CBD oil and testosterone at the time.
Although a review of 2020 preclinical studies from the PubMed database suggests that "it can be concluded that the CBD has a negative effect on the male reproductive system," the authors were very clear that more research is needed to see if these less-than-beneficial findings apply in humans and at what doses.
What is testosterone?
Testosterone, sometimes referred to simply as "T", is a male reproductive hormone produced mainly in the testicles. Although it is most often considered a male hormone, it is also produced in small amounts in women. It is responsible for many important functions, including sex drive, fertility, fat storage and burning, muscle mass, red blood cell production and even mood regulation.
Most of us are familiar with the biological changes that occur in boys at the onset of puberty, and it probably won't come as a surprise to hear that the dramatic increase in testosterone production is responsible for the deepening of the voice, body hair, increased muscle mass, growth of the penis and testicles, and sperm production.1
In fact, during adolescence and into the twenties, testosterone levels peak, followed by a slow decline accelerated by factors such as alcohol consumption, exposure to toxins, obesity, heavy metals and pesticides. Symptoms of low testosterone in men include low libido, erectile dysfunction, fatigue, depressed mood, loss of muscle strength and brain fogginess.
Illicit drug use is often added to the list of contributing factors, but interestingly commonly prescribed painkillers such as prescription opioids and even ibuprofen can also prematurely reduce testosterone levels in young men.2
Although we generally think of testosterone as a male hormone, it is also found in women and conversely, estrogen can , a form of the female hormone estrogen, also plays an important role in male sexual health. Although they are present, they occur in different amounts in men and women, and indeed, it is these gender differences in our hormones that experts believe may contribute to the differences in how men and women feel about marijuana.
Marijuana, testosterone and the endocannabinoid system
The average cannabis consumer probably doesn't spend much time thinking about the biology behind the sensations they experience when consuming pot.
In fact, it wasn't until the 1990s, when scientists discovered the endocannabinoid system (ECS), a vast network of special receptors in our brains and bodies that are activated by marijuana-like chemicals, that even the scientific community began to understand the intoxicating effects of marijuana. It was realized that THC fits into these receptors like a key that opens a lock, which in turn causes a cascade of effects throughout the body.
The endocannabinoid system itself is understood as a regulator of homeostasis, constantly working to maintain balance in all physiological systems. Not only can endocannabinoid receptors be found in the male reproductive system, such as the testis, prostate, vas deferens and spermatozoa, but other components of the ECS, such as the endocannabinoid anandamide and the enzyme responsible for its degradation, fatty acid amide hydrolase (FAAH), have also been localized in testicular tissues. 3
The fact that the leydig cells from which testosterone is released also contain CB1 endocannabinoid receptors led the researchers to conclude that ECS plays an important role in maintaining healthy levels of testosterone production.
Interestingly, a 2001 study in mice found that anandamide, which acts similar to THC by binding to CB receptors, inhibits testosterone levels, perhaps fueling the theory that THC must do the same. 4
THC and testosterone - the evidence
While many preclinical animal studies have suggested that THC administration lowers testosterone levels, human studies have been far less conclusive and have failed to prove that marijuana lowers testosterone.
In a 2018 study aimed at estimating the impact of marijuana consumption on American men, 1,577 men were asked about the frequency of marijuana use and compared it to serum testosterone levels.
No difference in testosterone levels was detected between men who had consumed marijuana at some point in their lives and those who had never tried it. However, serum testosterone levels were higher in men who had recently consumed marijuana, indicating that any changes are related to how recently the marijuana was consumed, rather than duration or frequency. 5
In Denmark, by contrast, a study of 1,215 young men found rather contradictory results regarding the effects of marijuana on men's reproductive health. On the one hand, sperm concentration and sperm count were almost 30% lower in weekly marijuana users, while, rather counterintuitively, testosterone levels were higher and in the same range as in cigarette smokers (smoking has been found to increase testosterone levels). Further research is needed to see what effect smoking marijuana with tobacco has on testosterone levels compared to other methods of consumption. 6
Can exposure to cannabis during pregnancy affect fetal testosterone levels?
One area that is sure to spark debate is whether marijuana is safe during pregnancy. While the jury is still out and evidence is lacking, one study sought to test whether giving THC to mice mothers-to-be on day 12 of pregnancy would affect testosterone levels in their male offspring. At least in that study, testosterone and luteinizing hormone levels were significantly reduced, while CBD administered on the same day resulted in suboptimal testicular weight.
For ethical reasons, this study is unlikely to be replicated in humans, but at least it raises awareness that what a mother consumes during pregnancy, be it cannabis or coffee, can have a direct impact on her baby.
Can marijuana use affect sex drive?
The fact that recent marijuana use appears to increase testosterone levels seems to turn on its head the theory that marijuana suppresses male libido.
Again, numerous animal studies, from rodents to primates, suggest that THC is at least somewhat of a passion killer. However, when it comes to humans, once again nothing has been conclusively proven.
Several studies have linked marijuana use to premature ejaculation and erectile dysfunction (ED), and when 8650 Australian men were surveyed about marijuana use and its sexual effects, daily use was correlated with poorer sexual and erectile performance. Women did not experience the same effects of marijuana use, and may even be more likely to reach orgasm if they use marijuana. 7
Correlation does not mean causation
As for marijuana and testosterone, it seems that this may be another case of correlation not implying causation. Yes, overall testosterone levels may be declining in the West, and male infertility may indeed be on the rise, but increased marijuana consumption is probably not the culprit, and certainly not the main reason. Instead, myriad factors, such as opioid abuse, pesticide use in cultivation and rising obesity levels, may play a role.
