Side Effects of Marijuana: An Overview


  • Marijuana can cause a number of short-term and long-term side effects
  • Short-term effects usually last for 1-2 hours
  • Frequent use may have long-term impact on cognition and mood, but research is inconclusive

Marijuana is commonly believed to be a safe drug due to the lack of overdose risk. But all drugs affect the body in some way or another, and research shows that marijuana is no different.
While the overall impact of cannabis is relatively minor, studies suggest users can be at risk of a number of short and long-term side effects.

The short-term effects of marijuana usually last for only 1-2 hours, beginning from when the drug is ingested. Depending on the individual, these may include:

  • red eyes
  • dry mouth
  • dizziness
  • fatigue
  • increased heart rate
  • psychosis

In addition, those who use marijuana frequently may experience the following long-term effects.


Feeling anxious or paranoid is one of the most common adverse effects of marijuana. Many report having panic attacks or bouts of anxiety after using cannabis, especially when taken in high doses. Studies confirm that marijuana acts on a region of the brain responsible for fear known as the amygdala.

Interestingly enough, marijuana has also been shown to reduce anxiety. Studies suggest that THC (tetrahydrocannabinol) – marijuana’s active ingredient – may have a ‘biphasic’ effect depending on dose. This refers to the fact that THC seems to reduce anxiety in low doses while increasing anxiety at higher doses.

Some strains of marijuana contain another compound called CBD (cannabidiol), which has more consistent anti-anxiety effects than THC.


Many studies have linked marijuana use to depression. Indeed, depression is more common among cannabis users compared to the general population. However, users of marijuana report that it has anti-depressant effects and animal studies seem to support this belief.

Overall, it remains unclear whether marijuana use leads to depression or whether depressed individuals are more likely to turn to marijuana for relief.

Memory Problems

A number of studies suggest that marijuana use may negatively impact cognitive function by interfering with memory. The most noticeable effect seems to be on short-term memory, although long-term memory is affected as well.

On the other hand, some studies suggest that memory and overall cognitive performance will return to normal levels after marijuana use is stopped.

IQ Loss

The effect of marijuana on IQ is widely debated, but a few studies have reported a link between marijuana use and a decrease in IQ.

One study, published in 2013, followed 1,000 people from birth to late adulthood and found that marijuana use was associated with an average 8-point drop in IQ. However, a following report published in the scientific journal Nature concluded that there is still not enough evidence to know whether marijuana can cause a drop in IQ.

Lung Symptoms

Marijuana can be taken in a variety of ways, but smoking is one of the most common.

Unlike tobacco, studies have failed to demonstrate a link between marijuana and lung cancer. Likewise, the largest study so far on cannabis smoking revealed no impact on lung function, even among the heaviest users.

Still, experts warn that smoking marijuana can deposit tar and irritate the airways, which may lead to minor respiratory problems like chronic bronchitis. Symptoms of chronic bronchitis include a persistent cough and increased phlegm production. The use of a vaporizer may help avoid these issues.


Marijuana use, like all recreational drugs, can lead to addiction. It is estimated that about 9% of marijuana users become addicted to the drug at some point. Compared to common substances like alcohol and tobacco, the rate of marijuana addiction is relatively low.

Marijuana addiction or dependence is characterized by the development of a tolerance and the experience of withdrawal symptoms. In other words, frequent marijuana users may find themselves needing more of the drug to achieve the desired effects and may experience difficulty when trying to quit.

Symptoms of marijuana withdrawal include irritability, anxiety, insomnia, decreased appetite and depression.

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