A lot has been speculated about marijuana’s influence on testosterone:

“Smoking weed causes man-boobs.”

“Cannabis use is associated with lower testosterone levels.”

“The THC in marijuana is estrogenic.”

“Smoking joints can make you infertile.”

This article will cut through the rumors, speculation, and personal anecdotes and get right down to what the science actually has to say.

You’ll learn everything you need to know about marijuana in the context of male health.

Ready?

Let’s do this.

The Link Between Weed And Gynecomastia (aka Man Boobs)

Gynecomastia (aka gyno) is the medical term for “man boobs” or “moobs”.

The link between cannabis and the enlargement of male breast tissue dates back to the early seventies, when a couple of case studies connected the two. It was suggested that marijuana is estrogenic and disrupts the hormonal balance in males.

Then, in 2013, an article was published by CNN linking cannabis use as a plausible cause of moobs. The report was endorsed by cosmetic surgeon Dr. Youn who took the case for a “plausible link” to a whole new level - for someone in the business of performing gynecomastia surgeries, of course, there would be a link.

The CNN article is what spurred a plethora of rumors and speculations that remain prevalent till today.

So what’s the truth?

Well, there is a test-tube study that shows compounds of marijuana to compete with estradiol (a significant estrogen) for binding to estrogen receptors. But when the same experiment was run using an animal model, researchers found neither an estrogenic nor anti-estrogenic effect. A cell-culture study on breast cancer cells also found no influence of marijuana on estrogen receptors.

But cell-culture and test-tube studies rarely have an implication on humans.

The only human study I was able to find on gyno and testosterone was performed in US army soldiers. The study reported no link between gyno and marijuana use, but the sample size of 11 men is way too small to draw any definitive conclusions.

Marijuana And Testosterone

The case for marijuana’s influence on gyno development is primarily attributed to a disruption in hormonal balance - precisely, the testosterone to estrogen ratio.

There are a couple of animal studies that support this:

When male rats were fed an aqueous extract of cannabis Sativa for 36-days, they experienced dose-dependent decreases in testosterone - 3mg of cannabis per kg of bodyweight slashed the rat’s testosterone levels in half, with further reductions seen in the rats given 6mg/kg.

In rat cell-culture studies, infusion of cannabinoids significantly decreased testosterone by inhibiting the activity of enzymes involved in testosterone synthesis.

If, after reading these studies, you’ve reached the conclusion that cannabis decreases testosterone, you’re right:

It does…

…in rats.

But do the same effects carry over in humans as well?

Some people make the case that rodents and humans have similar reproductive systems and that, therefore, the results from animal studies can be extrapolated on to humans as well. But from what I’ve reviewed after reading thousands of research studies (literally), this is not usually the case.

When extrapolating the results from scientific studies, it’s always best to go off research performed in humans. Even then, you should look at factors such as experimental design, number of subjects, and length of the experiment to make sure that the results are actually applicable to you and not just in a small cohort of individuals.

The following are six human studies that observed the influence of marijuana on testosterone:

a) In men, an intravenous infusion of 10mg of THC - the active ingredient in marijuana - over 50 minutes showed a time-dependent decrease in testosterone. When compared to the control group, the subjects had 36% lower testosterone levels. In the same experiment, a separate group of subjects smoked a marijuana cigarette, after which their testosterone level dropped to 66% of their baseline value.

b) 4 healthy male volunteers were brought into a lab and assessed for hormonal concentrations before and after smoking marijuana cigarettes containing 2.8% THC. A significant reduction in LH (a precursor for testosterone) was noted after smoking, while FSH (another precursor for T) and testosterone levels were only slightly suppressed.

c) A study using isolated THC on 17 male volunteers over 4-days found no alteration in cortisol, LH, or testosterone levels.

d) Testosterone measurements were assessed in 25 male university students who regularly smoked weed (minimum of 1 time per week with an average of 5.1 joints per week). When compared to 13 non-smoking control subjects, the marijuana smokers’ testosterone levels were about the same.

e) 93 men and 56 women (average age=23.5) were brought into a lab and assessed for various hormonal parameters (LH, FSH, testosterone, cortisol, and prolactin). Subjects were grouped based on their frequency of marijuana use - frequent, moderate, and infrequent. Compared to the 75-non smoking control subjects, no significant differences in hormone concentrations were noted in either men or women across all groups.

f) 20 male subjects (aged 18-28) who smoked weed at least 4-days per week for a minimum of 6-months were brought into a lab. The average testosterone level in these subjects was 44% lower (416 ng/dL versus 742 ng/dL) compared to the control group who never used cannabis.

Of the six studies cited above, three show a decrease in testosterone after marijuana use, while the other three show no effect.

Keep in mind that your testosterone level is not just one number. Testosterone secretion fluctuates rapidly based on several factors like the time of day, whether you’ve eaten any food, whether you’ve worked out, how much sleep you got the previous night, etc. Smoking weed is just one of the many factors that may also have an influence.

The following section discusses some possible mechanisms of marijuana’s negative influence on T.

How does marijuana decrease testosterone?

A review study published in 1984 theorized that marijuana inhibits testosterone due to the GnRH-blocking effects of THC.

GnRH (gonadotropin-releasing hormone) is what triggers the production of testosterone. It is produced in the hypothalamus and makes its way to the pituitary gland. It stimulates LH production (luteinizing hormone) and FSH (follicle-stimulating hormone) - the precursors for testosterone.

Study f cited above supports this theory - when the marijuana smokers were administered with hCG (human chorionic gonadotropin), their testosterone levels elevated towards normal.

Another mechanism through which cannabis may decrease testosterone is via increased cortisol production.

In study b cited above, the subjects smoking up to two joints experienced significant cortisol elevations. This effect was noted in another study (17), where intravenous THC increased cortisol levels in a dose-dependent manner. The increase, however, was blunted in regular cannabis users.

Cortisol is the hormone your body releases during times of stress. It is manufactured from the same raw material as testosterone, and therefore higher cortisol levels are associated with lower testosterone. But it should be noted that there is no long-term change in the rhythm of cortisol release in cannabis users versus non-users, as was shown in study c cited above.

All of this brings us to the next question…

Can smoking weed increase testosterone?

If you’ve seen Pumping Iron, you’ll recall the infamous scene where Arnold is puffing a joint in celebration of his 1975 Mr. Olympia championship.

Which begs the question:

If weed decreases testosterone, how did Arnold smoke pot and still manage to win 7 Mr. Olympia Titles?

Interestingly some studies show chronic marijuana use to be correlated with higher testosterone:

1) 27 men (aged 21 to 26) were brought into a lab and assessed for their testosterone level before, during, and after 21-days of marijuana use. The average testosterone level for casual users (smoked 54 joints over 21 days) was 988 ng/dL. The average testosterone level for the heavy users (smoked 119 joints over 21 days) was 1115 ng/dL. Both casual and chronic users were found to have testosterone levels near the normal range’s upper limit.

2) A study of 1,215 Danish men (aged 18-28) also shows long-term cannabis use to be associated with higher levels of both total and free testosterone.

And then we have Elliot Hulse, renowned strength coach and powerlifter, who talks about how smoking pot allowed him to feel more relaxed and lift more weight:

So what’s the takeaway from this - that smoking weed can help build muscle?

Well, not quite.

To address Arnold’s point, it’s important to note that even though he smoked pot during his time as a world champion bodybuilder, there’s another factor that we have to consider as well - steroids. Even if smoking pot negatively affected his T, that effect was offset many times over by a drug way more powerful.

To address the findings of the two studies cited above:

Although marijuana users were shown to have higher testosterone, the variance between users and non-users was not statistically significant.

Check out this article by Sean Nalewanyj for a more in-depth look at marijuana’s influence on muscle building.

Does Smoking Weed Kill Sperm?

Though marijuana’s effect on testosterone is inconclusive, its impact on seminal parameters is straightforward.

One of the longest and most robust studies on this topic occurred between 2008 and 2012 in Denmark.

1,215 men (aged 18-28) were recruited and went through compulsory medical examinations to determine their fitness for military service. The subjects offered semen samples and blood samples. They were put through numerous physical tests as well.

Of particular interest to us is that each of these men was categorized into 3 groups based on their usage of marijuana - 1) no use, 2) use once per week or less, or 3) use more than once per week.

45% of the men had smoked marijuana within the last 3-months.

When observing the entire sample of subjects, researchers found that the subjects who smoked marijuana for more than once per week in the 3-months prior had 28% lower sperm concentrations and 29% lower sperm count compared to the overall sample size.

Similar results were found in another long-term study that found cannabis to be a risk factor for poor sperm morphology.

To Smoke Or Not To Smoke?

That is the question.

Based on the research, smoking weed, in itself, is not likely to alter your testosterone levels. But what can mess with your hormones is the effect that smoking weed has on you.

For example:

Smoking weed makes many people lazy and unproductive. I definitely won’t be making it to the gym after a doobie, but I will be more likely to munch on ice cream, cookies, Cheetos, and other foods that I know I shouldn’t be eating.

But if smoking a joint doesn’t mess with your ability to stick to your regular diet and exercise routine, I don’t see any reason why it should alter your muscle building and fat-loss efforts.

Weed affects everyone differently. What it comes down to, at the end of the day, is personal preference.

But the final point to keep in mind is that marijuana does seem to harm sperm quality - if you’re trying to have a kid, lay off the herb.

What’s your opinion on the topic of marijuana and testosterone?

How has smoking weed affected your progress in the gym?

Thanks for reading.
David, RN, CCRN