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4 Long-Term Effects of Smoking Marijuana

4 states—Alaska, Colorado, Oregon, and Washington—and Washington D.C. have legalized marijuana. With these changes in policy, a big question on everyone’s mind is, what are the long term effects of marijuana use? How does marijuana use affect the body and mind over time? Is it safe?

Unfortunately, there isn’t a lot of research into the long-term effects of marijuana. This makes it difficult to make conclusions about marijuana’s long-term impact. However, we can look at research on animals and humans for more information on how marijuana affects the mind and body.

Read on to learn more about the 4 Potential Long-Term Effects of Smoking Marijuana.

#1: Changes in Brain Function

It’s quite possible that smoking marijuana could cause long-term changes in your brain.

The strongest chemical in marijuana, which comes from the cannabis plant, is delta-9-tetrahdrocannabinol (THC). When you smoke marijuana, THC binds to cannabinoid receptors in your brain.

In animal studies, when young rats were exposed to THC they had problems with memory and learning later in their life (NIDA, 2016).

Another study found that when young rats were repeatedly exposed to marijuana they had trouble forming new memories as they transitioned into adulthood. The rats in this study also had more anxiety and less desire to interact socially (O’Shea, Singh, McGregor, & Mallet, 2004).

What can we gather from studies like these? When your developing brain is exposed to marijuana it could possibly cause long-term and permanent changes to your cognitive functioning and behavior.

#2: Lung Damage

As you may have guessed, smoking marijuana can damage the lungs. Although some studies suggest that long-term marijuana use can have similar effects on the lungs as cigarette smoking, we cannot make conclusions based on current research.

A study conducted by researchers at the University of California, San Francisco found that marijuana is not as damaging to the lungs as tobacco. In their study, occasional marijuana use was not linked with damage to the lungs. However, their study did suggest that heavier marijuana use may increase the risk for lung damage, but they did not have enough heavy marijuana smokers in their study to make that conclusion (Pletcher et al. 2012). Limitations in studies such as this are pretty common in the marijuana research community.

While their research doesn’t prove that smoking marijuana can lead to lung cancer or serious lung damage, you’re still exposing your lungs to smoke, which can lead to lung problems, such as chronic bronchitis.

#3: Damage to the Reproductive System

Marijuana may also affect your reproductive system, regardless of whether you’re a male or female.

With male infertility on the rise and 15% of couples unable to get pregnant (Eisenberg, 2015), researchers are beginning to ask whether marijuana use could be contributing factor (du Plessis et al., 2015). However due to a lack of research into the topic, this remains unclear. (Noticing a trend yet?)

In animal studies, males exposed to marijuana produce less testosterone. And in human studies, researchers have also found that THC negatively affects the production of testosterone. THC has been found to reduce sperm motility, or a sperm’s ability to swim properly, which also contributes to male infertility (Fronczak, Kim, & Barqawi, 2012).

Researchers have found that marijuana has affects on female rats too. When they were exposed to marijuana, the rats produced less female sex hormones, like progesterone and estrogen. If you’re a woman, producing less sex hormones may lead to sexual dysfunction and your ovulation cycle may also be affected.

These studies of the effects of marijuana on female fertility have also been inconclusive, and the research community does not known how much disruption of the reproductive hormones is needed to result in changes in fertility and sexual function.

Here’s another thing to remember if you’re female—if you’re pregnant, heavy marijuana use can be risky as THC can negatively affect fetal growth and development (Smith & Asch, 1984).

#4: Anxiety and Depression

If you’re an adolescent, you should be extra careful when smoking marijuana, as you may be prone to developing anxiety and depression.

Human studies have found, to varying degrees, that early marijuana use is associated with risk for anxiety and depression. However, the relationship is complex and poorly understood.

Some studies suggest that if you carry certain genes you may be at increased risk for developing a psychiatric disorder, like schizophrenia if you use marijuana. Some studies also found that there are certain genes that make you more prone to developing psychosis if you smoke marijuana. Not surprisingly, the amount you smoke will increase your risk of psychosis. In fact, the risk for psychosis was 7 times higher for daily marijuana users than less frequent or non-users among these specific gene carriers (NIDA, 2016; Caspi et al. 2005).


More and more people, especially teens, are using marijuana. With an estimated 22.2 million current marijuana users aged 12 or older in the United States, it is a concern that we have relatively limited information about how marijuana affects the brain and a person’s susceptibility to psychiatric disorders.

According to the National Institute on Drug Abuse (NIDA), the National Institutes of Health (NIH) is funding a major longitudinal study that will track a large cohort of young people and their marijuana use through adulthood (NIDA, 2016). Not only will this study examine the long-term effects of marijuana and THC, but it will provide insight on how the drug affects an adolescent’s brain development.

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