Can Marijuana Make you Blackout?

In our latest question and answer, our cannabis expert discusses what exactly a blackout is and whether or not marijuana can make you blackout.
Can Marijuana Make you Blackout?

Alex Asked

Can marijuana make you black out? My friend said they know someone that fainted after smoking.


Cannabis won’t make you blackout the way that alcohol will, but it can cause short term memory loss, make you fall asleep, and in rare cases faint.
You should be aware of the signs and symptoms that may precede fainting such as dizziness or feeling lightheaded.
If your symptoms persist, it’s best to consult a medical professional. Decreasing your dose of THC and sitting down and getting up slowly may help avoid this.
More research is needed to determine cannabis’ effects on brain function and memory especially at higher doses.v


Thanks for your question Alex. While cannabis is well-known for its beneficial effects, as with any drug, users may experience unwanted effects from time to time. These can range from minor side effects that are only bothersome in nature to severe adverse events requiring medical attention. Some unwanted effects from cannabis we’ll discuss below include memory loss or blacking out, drowsiness, and fainting.

What is a “Blackout”?

A “blackout” is a term used to describe a temporary loss of consciousness or memory. Usually the term is used to describe a state brought on by excessive alcohol consumption or combining alcohol with other drugs. In the case of alcohol-induced blackouts, these occur when a rapid increase in blood alcohol concentration interferes with the function of the hippocampus, a region of the brain responsible for learning and memory. What’s interesting about an alcohol-induced blackout is that the person experiencing the blackout may be capable of using the rest of their brain. A person that’s completely blackout drunk may still be able to carry out a conversation, complete simple tasks, or even drive a car with absolutely no memory of doing so. If you’re ever wondering if someone is blackout drunk, just keep asking them the same question over and over again. If they answer you every time and don’t address the fact that you keep asking them the same question they’re likely experiencing a blackout. 

Can cannabis cause a black out?

Cannabis doesn’t work the same way that alcohol does in the brain, as such, it doesn’t cause total memory blackouts the way that alcohol does. However, cannabis can definitely still cause problems with memory and even temporarily cause you to lose consciousness, but not usually to the extent seen in an alcohol-induced blackout. It’s well-known that cannabis can cause somnolence (drowsiness) and syncope (fainting). Both of these side effects can vary in magnitude, and may be referred to as “blackouts” depending on the use of the word. 

What is Somnolence?

Somnolence or drowsiness is feeling sleepy or like you’re ready to fall asleep. The reason that I mention cannabis can cause somnolence is because when this side effect is combined with cannabis’ negative effects on memory it can sort of resemble a blackout. For instance, let’s say you consume cannabis and following that you get drowsy and fall asleep. Then, you wake up hours later wondering where the time went or what happened to you before you fell asleep. You might not even remember laying down or falling asleep at all. While the situation I just described isn’t exactly the same as an alcohol induced blackout or a loss of consciousness it’s similar in that there was some partial memory loss.

What is Fainting?

Fainting or “syncope” is a brief loss of consciousness (and posture) with a sudden onset. Although the loss of consciousness from fainting is usually quite brief, it may also be accurately referred to as a blackout. Usually if a person is standing when they faint, they’ll fall down. This can be dangerous for obvious reasons. Fainting is most commonly caused by decreased blood flow to the brain. People with pre-existing health conditions that use cannabis may be at increased risk of fainting. For instance, if you’ve had problems with low blood pressure called hypotension, you might be more likely to faint after using cannabis. This is because tetrahydrocannabinol (THC) in cannabis is a potent vasodilator. This means that it causes blood vessels to expand, lowering blood pressure and causing your heart rate to increase. If sufficient blood does not reach your brain, you may become lightheaded or feel dizzy. In severe cases these effects might even result in a syncopal episode, more commonly called fainting.  

Factors Affecting the risk of a Blackout

Mode of Consumption

How you consume cannabis can affect your risk of blacking out. Smoking a joint, a bong, or vaporizer achieves higher blood THC concentrations within a shorter period of time. If you’re new to cannabis, or just not familiar with the effects from inhaling it, you might be more likely to experience some of the effects mentioned above. But again, fainting is pretty rare unless you have preexisting conditions. 


Blacking out is also related to the potency of cannabis. The higher the potency, the greater the chances of blacking out. This is especially true for inexperienced smokers as they’re more likely to be sensitive to the effects of THC. 

Underlying Health Conditions & Combining Cannabis with Other Drugs

Blacking out can also result from an underlying medical condition, or from combining cannabis with other medications. For instance if you have diabetes, heart problems, or problems with blood pressure, you might be more susceptible to the above effects. A 2002 study showed that when patients with cardiovascular diseases consumed high amounts of THC, they were at a higher risk of fatally increasing their catecholamine levels, as well as suffering from carboxyhemoglobin and postural hypotension. Conditions such as hypotension and hypoglycemia can also increase your chances of passing out after consuming cannabis. Moreover, when cannabis is combined with other CNS depressant drugs like alcohol, benzodiazepines like xanax, or opioids; negative side effects like somnolence and memory loss from cannabis may be more pronounced.

Black Out and Memory Loss or Impairment

In some cases, cannabis can cause short term memory loss or “blackouts”. Acutely intoxicated individuals may have difficulty recalling words, where they put their belongings, or other bits of information they wouldn’t normally forget. This ‘amnesia’ or memory loss tends to worsen if the user drinks alcohol or combines cannabis with other psychoactive drugs. But again, this is different from the total memory loss that may be seen when blackout drunk from alcohol. 

With time, heavy cannabis use can take a severe toll on cognitive function, making the user feel fuzzy-headed and experience difficulty remembering things and focusing. According to a 2012 study published in the Proceedings of the National Academy of Sciences of the United States of America, young adults who smoked cannabis heavily lost IQ points.

Be Prepared

When you consume cannabis there are some signs that are likely to occur prior to experiencing one of the above symptoms. If you learn to recognize them early on, you can reduce the risk of harm associated with them. 

  • Dizziness
  • Nausea
  • Headache
  • Blurred vision
  • Shortness of breath 
  • Paleness of skin
  • Looking or feeling unresponsive 

If you start experiencing some or all of these symptoms, find a safe place where you can calm down and allow your body (and mind) to adjust to the effects of THC. If you’re able to lay down and fall asleep, simply sleeping it off may help. Remember that most harmful effects due to cannabis are quite rare unless you have serious preexisting conditions. Obviously do not hesitate to seek medical attention if you think your situation is more serious. 

Preventing Negative Effects from Medical cannabis

Many patients will not tolerate fainting or memory loss as a side effect of cannabis. Here are some techniques that might help you prevent this from happening. 

  • Lowering your dose of THC. THC is a vasodilator, so opting for a product with a lower dose of THC might limit these effects and minimize the chances that you’ll experience fainting, memory loss, or somnolence. Doctors even recommend THC-free formulations for some conditions.
  • Use caution when getting up after sitting down for a long time after using cannabis. Standing up quickly increases the risk of fainting, especially if you have certain pre-existing problems with blood pressure such as orthostatic hypotension.  
  • Getting some fresh air may also help thwart feelings of lightheadedness or dizziness.

I hope this helps answer your question Alex! Please feel free to reach back out to us at anytime. 

  1. Alcohol-Induced Blackout link.
  2. Overbaked: assessing and predicting acute adverse reactions to Cannabis link.
  3. An Evidence-Based Review of Acute and Long-Term Effects of Cannabis Use on Executive Cognitive Functions link.
  4. The effect of cannabis use on memory function: an update link.
  5. Association Between Lifetime Marijuana Use and Cognitive Function in Middle Age link.
  6. Postural syncope after marijuana: a transcranial Doppler study of the hemodynamics link.
  7. Alcohol, Memory, and the Hippocampus link.
  8. Effects of Smoking Marijuana on Brain Perfusion and Cognition link.
  9. Cardiovascular system effects of marijuana link.
  10. Persistent cannabis users show neuropsychological decline from childhood to midlife link.

Was this article helpful?

Related Questions

Go To Top