Smoking marijuana can be relaxing, but men don't want to be too relaxed when it's time for some frisky business. So it's no surprise that people are concerned about weed dick - the possibility that smoking too much marijuana will cause erectile dysfunction. Basically, you get high while your little guy stays low.

On the flip side, some think that the psychoactive elements of marijuana (e.g., Δ9-THC) actually enhance sexual pleasure. In fact, patients of the Haight-Ashbury Free Medical Clinic back in the 70’s claimed that smoking a joint improves the sexual experience.

But what does the research say about 'getting it up' on cannabis?

More than you ever wanted to know about erections

Before discussing cannabis, let's do a quick overview on the science of erections.

An erection results from the relaxation of the smooth muscle of the corpus cavernosum in the penis. Basically, the relaxation of the smooth muscle increases blood flow, causing an erection. Conversely, preventing the smooth muscle from relaxing causes ED. That's why drugs like Viagra work by enhancing the muscle's relaxation and prolonging erections. (Brace yourself: there are way more unintentional puns coming your way.)

A chain of events must occur before that smooth muscle relaxes. First, cells in the penis receive sensory input from sexual stimulation or from signals originating in the brain. Activation of these cells causes the production of a gas called nitric oxide. Nitric oxide acts as a signalling messenger to a variety of targets - including the enzyme cGMP, which has to be activated before an erection can occur. When nitric oxide production stops, the cGMP enzyme inactivates, the smooth muscle stops relaxing, and the erection goes away.

Your penis on pot

Cannabinoid receptors, which are activated by Δ9-THC, are found both in the brain and periphery. In the brain, Δ9-THC activates cannabinoid receptors and makes you feel stoned, but in other parts of the body, it can have diverse effects. And you guessed it, the corpus cavernosum has cannabinoid receptors.

Δ9-THC does not discriminate. When you consume weed, either by smoking, vaping, or eating, eventually that Δ9-THC makes it into your blood stream where it hits the brain as well as the penis. Unfortunately, research restrictions on marijuana have impeded laboratory studies of cannabis and human erections, so we're stuck with having to infer marijuana’s potential effect from indirect evidence.

Scientists have found that activating cannabinoid receptors with the endocannabinoid anandamide enhanced the relaxation of the corpus cavernosum's smooth muscle in rats and rabbits. In a follow-up experiment, researchers found that blocking the cannabinoid receptors inhibited relaxation of the corpus cavernosum. So it seems that getting an erection hinges on at least some activation of these cannabinoid receptors in the body.

But there's a hitch. It turns out that anandamide has the opposite effect in monkeys. In one study, anandamide inhibited the relaxation of the smooth muscle, which suggests that Δ9-THC promotes erections in rodents but prevents erections in monkeys and possibly humans (but we'd have to test that out on people to know for sure).

Your brain on cannabis

Δ9-THC may affect erections by activating cannabinoid receptors in the brain as well as in the penis. In the absence of physical stimulation, erections can't occur without the release of the hormone oxytocin, which is controlled by a part of the brain called the hypothalamus. 

Researchers have found that blocking cannabinoid receptors in the hypothalamus causes erections in rats. Some think that blocking these cannabinoid receptors increases oxytocin release, which in turn, leads to an erection. Keep in mind, however, that these findings don’t necessarily mean that activating cannabinoid receptors with Δ9-THC would prevent an erection (more studies are necessary to prove that).

But current research does provide an important link between the body’s cannabinoid system and ED. Whether marijuana itself causes ED is still uncertain though.

Human studies

Unfortunately, human studies are just as inconclusive as the animal ones. In one longitudinal study from the 1980s, regular marijuana users reported that cannabis enhanced their sexual experience. Their feedback remained unchanged in a follow-up interview 6-8 years later. So based on that study, it doesn't seem like cannabis induces ED in humans.

However, a conflicting report published in 1982 found that the prevalence of ED was twice as high in daily marijuana users as non-users. Researchers found that habitual marijuana use was associated with dysfunction in the cells of the corpus cavernosum that produce nitric oxide. If you reduce nitric oxide production in these cells - as the researchers claim was the result of habitual marijuana use - then no erection.

Those are just two examples of the contradictory findings that have surfaced over the years on this subject. These inconsistencies likely stem from the variation in surveying methods. For example, many studies look broadly at the sexual response, which includes desire, excitement, and orgasm. It’s hard to pin-down marijuana’s effects on ED from a general survey on sexual behavior.

To try and gain better insight into ED, researchers in the 90s developed an evaluative tool called the International Index of Erectile Function (IIEF). This tool gave them a way to objectively compare the spectrum of sexual function and ED. For instance, researchers could collect and compare IIEF scores between marijuana users and non-users. Using this IIEF scoring system, marijuana users were found to have similar IIEF scores as non-users. However, cannabis users were more likely to have severe ED than non-users.

But even those findings aren't conclusive due to inconsistencies among cannabis consumers. Simply put, people who identify themselves as cannabis users don't consume marijuana as much or as frequently as others. Figuring out the best way to manage those variables continues to plague researchers on the subject.

In an attempt to control for general use patterns, an Australian team once screened 4350 men for marijuana use levels and ED. Marijuana users were divided into three groups: daily use, weekly use, or less than weekly use. The researchers failed to find a link between marijuana use in any of the groups and ability to maintain an erection. But overall, this was an insufficient attempt to control for quantity of marijuana consumption as the frequency of marijuana use does not equal quantity consumed.

So right now, there’s very limited evidence from human trials to suggest that marijuana has either a positive or negative effect on ED. 

The future of cannabis/ED studies

Future assessments should extend beyond just smoking frequency, and control for amount of marijuana consumed. Obviously, someone that takes a couple of hits before bed every night is consuming far less than someone smoking multiple times throughout the day. Yet, in the Australian study discussed above, they would have been placed in the same group.

The method of consumption is also critical. The rate at which a drug hits the bloodstream and is metabolized vastly impacts the long-term effects it has on the body. Therefore, eating marijuana regularly (as is common for many medicinal users) may have different long-term impacts on the cells impacting ED than someone who smokes marijuana. Of course, the direction of this effect at the current time is unknown.

Additional lifestyle factors beyond just marital status play a role in whether marijuana could be associated with ED. If one smokes marijuana to alleviate work stress, then is it work stress that causes ED or marijuana? The studies to-date can’t differentiate between the two factors.

Health factors such as age, cardiovascular disease, and diabetes all increase risk of ED. While age is controlled for in these studies, cardiovascular disease and diabetes are often not. Many additional health factors need to be included in these assessments than are currently considered.

Conclusion 

So, is there an equivalent of “whiskey-dick” when it comes to marijuana, or “weed dick” if you will? The animal research only proposes a mechanistic link between Δ9-THC and ED, and the human studies remain inconclusive. Until better research methodology is employed, the jury is hung.