Does Cannabis Lower Testosterone? What the Evidence Actually Shows

He is 29, smokes most evenings to switch off, and has done for years. A friend sent him an article saying weed wrecks testosterone, so he paid for a private blood test, fully expecting bad news.

His testosterone came back at 21 nmol/L. Solidly normal. He took it as proof the whole thing was a myth.

On testosterone, he was mostly right. On the question he had not thought to ask, whether it was affecting his sperm, his erections or his sleep, the answer is less comfortable.

Where the fear started

In 1974, the New England Journal of Medicine published a small study by Kolodny and colleagues reporting lower testosterone in young men who used cannabis heavily. It was widely reported, and it set the tone for decades.

The same journal published a study by Mendelson and colleagues the same year that found something different: men who smoked cannabis daily under observation on a research ward showed no fall in testosterone.

That pattern, one study finding an effect and the next finding none, has continued ever since. What has changed is the size of the studies.

What the larger studies found

Testosterone

The largest Danish study, by Gundersen and colleagues in 2015, examined 1,215 young men aged 18 to 28 at their military fitness assessment. Men who used cannabis more than once a week had slightly higher testosterone than non-users, in a similar range to cigarette smokers.

A study of men at a Boston fertility centre by Nassan and colleagues in 2019 found the same direction: greater cannabis use went with higher testosterone.

An analysis of American men in the NHANES survey by Thistle and colleagues in 2017 found no evidence that users had lower testosterone.

And a 2021 meta-analysis by Belladelli and colleagues pooled nine studies, with hormone data from 4,787 men. There was no significant difference in testosterone or LH between users and non-users. FSH was slightly lower in users, a difference the authors judged too small to be clinically important.

The honest conclusion: for most men, cannabis is unlikely to be the reason for a low testosterone result. If yours is low, the usual suspects deserve a look first, and our guide to what causes low testosterone lists them in order of how common they are.

Sperm

This is where the evidence gets more uncomfortable, and more confusing.

In the same Danish study of 1,215 men, those who used cannabis more than once a week had 28 per cent lower sperm concentration and 29 per cent lower total sperm count than non-users. In men who combined regular cannabis with other recreational drugs, the reductions were 52 and 55 per cent.

The Boston fertility centre study found the opposite. In 662 men, those who had ever smoked cannabis had an average sperm concentration of 62.7 million per millilitre, against 45.4 million in men who never had. Only 5 per cent of users fell below the WHO threshold of 15 million, against 12 per cent of non-users.

The authors of that study offered two explanations. Low levels of cannabis might act on the body's own cannabinoid system in a way that supports sperm production, or men with naturally higher testosterone may simply be more likely to try cannabis. They also pointed out that these were men at a fertility clinic, and that use may have been underreported.

The 2021 meta-analysis did not find a statistically significant link between cannabis use and impaired semen quality overall, but the studies were few and very different from each other.

So which is it?

Nobody can say for certain, and anyone who tells you otherwise is overstating the evidence. What we can say is that the largest general-population study found a meaningful drop with regular use, the fertility-clinic study did not, and the pooled data is too thin to settle it.

Given that, if you are trying for a baby, stopping for three months is a sensible and low-cost precaution. Three months matters because that is how long new sperm take to form, as explained in sperm count: what lowers it, what raises it, and the 74-day rule.

Why it could affect hormones at all

Your body has its own cannabinoid system, with receptors in the brain regions that control reproductive hormones and in the testes themselves. THC, the main active compound in cannabis, acts on those same receptors.

In animal studies, THC can suppress the signals from the brain that drive testosterone and sperm production. In humans, the picture is far less clear, possibly because of tolerance in regular users, differences in dose, or the fact that people who use cannabis differ from people who do not in many other ways.

The tobacco problem

In much of Europe, cannabis is often smoked mixed with tobacco. That matters, because tobacco smoking is independently linked to poorer sperm quality. Some of what gets blamed on cannabis may be the tobacco it is rolled with, and some of what gets attributed to tobacco may partly be cannabis. If you smoke joints with tobacco, you are exposed to both.

Erections

This is the effect men are least likely to connect to cannabis.

A 2019 meta-analysis by Pizzol and colleagues pooled five studies with 3,395 men. Erectile dysfunction was reported by 69.1 per cent of cannabis users against 34.7 per cent of non-users, and the odds of erectile dysfunction were almost four times higher in users.

The authors were clear about the limits. The studies were small, the confidence intervals were wide, and the design could not show which came first. Men with erection problems may use cannabis to cope, rather than cannabis causing the problem. Even so, it is a consistent signal worth taking seriously, because erectile problems are also an early warning sign for heart and blood vessel disease.

If erections have become less reliable, our guides to low testosterone and erectile dysfunction and morning erections and testosterone explain what to check, and the erection health check is a quick place to start.

Sleep

Many men use cannabis specifically to fall asleep, and it can help with that in the short term. The trade-off shows up when you stop: withdrawal commonly causes poor sleep, restlessness and vivid dreams for a period of days to weeks, which is part of why regular users find it hard to take a break.

Sleep matters directly for testosterone, which is produced largely overnight. If cannabis has become the only way you can fall asleep, that is worth addressing on its own terms. Our guides to the 90-minute sleep rule and sleep apnoea and testosterone cover the sleep problems most often behind low testosterone.

Mood and motivation

Low testosterone and heavy cannabis use can both show up as low mood, low drive and a sense of flatness, which makes them easy to confuse. If that sounds familiar, low testosterone and depression explains how to tell them apart.

One risk deserves a clear mention. A large European study by Di Forti and colleagues found that daily cannabis use, and especially daily use of high-potency cannabis, was linked to substantially higher odds of psychotic disorder. The risk is concentrated in heavy, high-potency use, and it is one reason to be cautious with modern strains.

What about CBD?

CBD products do not contain meaningful amounts of THC and do not produce a high. There is very little human research on CBD and testosterone either way, so there is no good basis for claims that it raises or lowers it.

What to do with this

If your testosterone is low and you use cannabis, do not assume cannabis is the cause. Get a proper morning testosterone test, repeat it if it is low, and look at sleep, body fat, alcohol and medications first.

If you are trying to conceive, stop for at least three months, and if you smoke it with tobacco, stop both.

If erections, sleep or mood have been slipping, try a proper break of several weeks and notice what changes. Expect the first week or two of sleep to be worse before it improves.

And if you are not sure whether your use has become a problem, the NHS and many local services offer confidential support.

Common questions

Does smoking weed lower testosterone?

For most men, probably not. The larger studies found normal or slightly higher testosterone in users, and a 2021 meta-analysis found no significant difference between users and non-users.

Does cannabis affect sperm count?

Possibly. The largest general-population study found that men using it more than once a week had around 28 per cent lower sperm concentration, but a fertility-clinic study found the opposite. If you are trying for a baby, stopping for three months is a sensible precaution.

Can cannabis cause erectile dysfunction?

Users report erectile dysfunction more often than non-users, with nearly four times higher odds in one meta-analysis. The studies cannot prove cause and effect, but the link is consistent.

How long after stopping cannabis does sperm recover?

Sperm take roughly 74 days to form, plus time to mature, so allow around three months before judging any change with a repeat semen analysis.

Does CBD lower testosterone?

There is very little human research on CBD and testosterone, so there is no reliable evidence either way.

Sources: Kolodny RC et al., Depression of plasma testosterone levels after chronic intensive marihuana use, N Engl J Med 1974;290(16):872-4 · Mendelson JH et al., Plasma testosterone levels before, during and after chronic marihuana smoking, N Engl J Med 1974;291(20):1051-5 · Gundersen TD et al., Association between use of marijuana and male reproductive hormones and semen quality, Am J Epidemiol 2015;182(6):473-81 · Nassan FL et al., Marijuana smoking and markers of testicular function among men from a fertility centre, Hum Reprod 2019;34(4):715-23 · Thistle JE et al., Marijuana use and serum testosterone concentrations among U.S. males, Andrology 2017;5(4):732-8 · Belladelli F et al., The association between cannabis use and testicular function in men: a systematic review and meta-analysis, Andrology 2021;9(2):503-10 · Pizzol D et al., Relationship between cannabis use and erectile dysfunction: a systematic review and meta-analysis, Am J Mens Health 2019;13(6):1557988319892464 · Di Forti M et al., The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe, Lancet Psychiatry 2019;6(5):427-36 · Educational only, not medical advice.

Keep reading: Sperm count: what lowers it, what raises it · What causes low testosterone · The truth about alcohol and testosterone · Medications that lower libido · Low libido in men · Low testosterone and depression