Fainting After Smoking Weed (Why It Might Happen and How to Prevent It)

fainting after smoking weed
By Anthony Pellegrino Updated March 8th

Medically reviewed by Dr. Brian Kessler, MD

Medical cannabis has many potential benefits, such as pain relief, increased relaxation, help sleeping, and the alleviation of nausea. But as with any substance, these results aren’t guaranteed for all users. And in some cases – especially at overly strong doses – marijuana has the potential to cause undesirable side effects.

Typically, any unwanted side effects are considered minor: lightheadedness, dizziness, or anxious thinking. However, while uncommon, some users report fainting after smoking weed.

No one wants to faint after using marijuana. Doing so can be embarrassing, or worse, dangerous to your health.

But how likely is it to faint after smoking? And how can you prevent it from happening to you?

In this article, we’ll look at everything you need to know about fainting and marijuana use: reasons why it might happen, and what you can do to ensure it never happens to you.

The Complete Guide to Medical Cannabis for Stress & Anxiety

Find natural, lasting relief with our comprehensive (and completely free) patient’s guide to medical cannabis for stress and anxiety.

Fainting After Smoking Weed: Typical Signs and Cases

What does it feel like if you’re at risk of passing out after smoking too much weed? People have reported the following symptoms before fainting:

  • Paleness or whiteness of the skin (aka the marijuana grays),
  • Tunnel vision
  • Ringing of the ears,
  • Nausea or vomiting,
  • Lightheadedness or dizziness,
  • Excessive sweating

Fainting: Is It a Common Side Effect or the Result of Smoking Too Much?

The most common side effects of smoking cannabis are fairly minor, and can include feeling dizzy or lightheaded. When a consumer has too much marijuana (or too strong a dose), those “light” symptoms can become more severe. And in rare cases, that can lead to fainting after smoking weed. Colloquially, you may have heard people refer to this as the “marijuana grays,” as people who may feel too lightheaded or at risk of passing out will often look white or gray.

After fainting, some people may experience symptoms similar to that of a weed hangover, such as headache, fatigue, or dry mouth. 

Fainting spells following marijuana use are not common and only typically occur in specific circumstances. But what’s the scientific reason that someone might faint after smoking?

4 Reasons For Fainting After Using Cannabis

reasons for fainting after smoking weed

There can be several reasons some people may have a higher risk of fainting following marijuana use compared to others. Here are the four primary causes. 

1. Vasodilation 

Researchers have noted that one of the most common reasons smoking cannabis could cause someone to faint is a sudden change in heart rate and blood pressure. 

Several studies have found that cannabis and THC can produce vasodilation as a side effect.¹ Vasodilation refers to the dilation, or widening, or your blood vessels.² When this happens, your blood pressure will decrease because more blood is able to flow through the blood vessels.

In most cases, a slight reduction in your blood pressure may not be all that noticeable. After all, vasodilation is a natural process in your body that occurs from time to time. However, a sudden drop in blood pressure could cause various symptoms, such as blurred vision, dizziness, or vasovagal syncope (fainting).³

Vasovagal syncope is a sudden drop in heart rate and blood pressure.⁴ It’s the same reason some people faint when they see the sight of blood or are in some sort of emotional shock. 

Conversely, THC has also been linked to increased heart rate and blood pressure immediately after smoking.⁵ 

These types of fainting spells are typically harmless, won’t require any medical attention, and people usually recover from them within a few minutes. Even so, it can still be a very unpleasant or scary experience. 

The Complete Guide to Medical Cannabis for Stress & Anxiety

Find natural, lasting relief with our comprehensive (and completely free) patient’s guide to medical cannabis for stress and anxiety.

2. Method of Consumption

Another more common cause of fainting after consuming marijuana is the method of consumption. 

Cannabis extracts are one common culprit of the marijuana grays. These products are high potency, with THC percentages listed as high as 90% or more.⁶ Users that aren’t used to such a strong dose – or who have lower weed tolerances – may experience uncomfortable levels of intoxication after using these products. Additionally, dabs and bong rips can call for consumers to take larger and longer breaths than they might normally, increasing the risk of fainting spells.

There are pros and cons to each method of consumption. Be mindful that just because you may be comfortable smoking a joint, you may not be ready to take high doses of edibles. 

The method of consumption extends beyond the product you use.

For example, taking a large inhale or ‘hit’ from a bong can leave you with less oxygen in your lungs. If you then stand up too quickly, it could cause a head rush (orthostatic hypotension). These head rushes could make you feel lightheaded, dizzy, or even cause you to faint.

No matter the method of consumption you choose, consider how it affects you to determine if another approach may help reduce the risk of unwanted side effects, like dizziness or fainting.

3. Standing and Smoking Weed

standing while smoking weed

Head rushes often occur because of the sudden drop in blood pressure resulting from standing up too quickly. However, cannabis can decrease blood pressure even if you’re already standing up when you start smoking. 

According to one study, “marijuana is known to cause symptoms suggestive of orthostatic hypotension, such as dizziness and fainting during upright posture.”⁷

If you’re worried about passing out after smoking weed, avoid smoking while standing up (and find a spot where you can sit and be comfortable for several minutes after smoking).

In most cases, head rushes are pretty mild and not a cause for concern. However, if they occur frequently or severely, you should always consult a qualified medical professional.

4. Using Contaminated Marijuana

Another reason that marijuana may cause people to faint after use is because of contamination. That is, weed mixed with, or exposed to other harmful materials or substances such as tobacco or formaldehyde.

The term “smoking wet” refers to the act of consuming these kinds of contaminated marijuana.⁸ “Wet” joints, for instance, are cannabis joints dipped in formaldehyde, phencyclidine, or both. This is extremely dangerous and can cause a variety of harmful effects, such as hallucinations, paranoia, brain damage, seizures, and fainting.

Similar distressing effects have been reported after consuming “spice,” an umbrella term for a variety of synthetic cannabinoid products that have been associated with an increasing number of toxic side effects resulting in trips to the emergency room.⁹

Fortunately, it’s very easy to avoid contaminated or synthetic marijuana products. 

Legal dispensaries and products are required to provide lab-test results so consumers know they’re clear of any toxic materials. You won’t ever find “wet” joints at a licensed dispensary. For that reason, it’s best to refrain from smoking with or accepting cannabis products from anyone you don’t know and trust.

If you think you’ve fainted because of your cannabis consumption, you should take one or more of the following steps to help reduce the risk moving forward.

How to Prevent Marijuana Fainting?

how to prevent fainting after smoking marijuana

While it’s true that cannabis may cause fainting spells, it’s an uncommon side effect, and most people recover fully within minutes. 

That said, there are several steps you can take to make fainting after smoking weed even more unlikely.

Opt for a Lower THC Strain

If you’re concerned with the possibility of fainting spells (if you’re a medical cannabis patient suffering from low blood pressure already, for example), it may be prudent to avoid especially high THC strains of marijuana.

Cannabis has changed a lot in recent decades. In fact, there has been an average increase in THC potency by over 200% since the 1990s.¹⁰

Likewise, it’s best to avoid any strain that leaves you feeling dizzy or disoriented. A strain’s combination of cannabinoids and terpenes could lead to stronger effects than you’d anticipated, regardless of THC levels. 

If you’re new to smoking weed or not used to potent strains, look for options with lower levels of THC or higher levels of CBD, a cannabinoid with no intoxicating effects.

If you need help finding the right strains, ask the budtenders at your local dispensary.

Ease Yourself Into Cannabis

For many consumers, dizziness and lightheadedness are the result of taking too high a dose. So the best way to prevent the marijuana grays is to start low and go slow: in other words, approach every new product or strain like you’re a beginner. Easing yourself into every smoke session is the best way to ensure that all your cannabis experiences are positive, enjoyable, and productive while reducing the risk of any adverse effects (fainting included).

Just because you didn’t pass out after smoking too much weed doesn’t mean that other negative side effects aren’t possible. Listen to your body when smoking or consuming marijuana. Remember to be patient, especially for edible products that may take a while to kick in.

The Complete Guide to Medical Cannabis for Stress & Anxiety

Find natural, lasting relief with our comprehensive (and completely free) patient’s guide to medical cannabis for stress and anxiety.

Drink Plenty Of Water

Finally, it’s always best practice to drink plenty of water while consuming cannabis.

When you’re dehydrated, it makes it more difficult for your body to circulate blood to vital organs. By staying hydrated, you can improve blood circulation and help prevent fainting spells

Not only that, drinking lots of water is one of the best ways to flush out THC from your system as quickly as possible.


Fainting is not a common adverse effect of marijuana use, but it can affect any consumer, regardless of their experience level. To reduce the risk of unwanted side effects, remember to ease into every session, stay hydrated, and stick to products you know can deliver the desired effects. 

None of the information in this article is a substitute for, nor does it replace, professional legal advice or medical advice, diagnosis, or treatment. If you’re a recreational or medical marijuana user and you’re concerned that cannabis use may be causing fainting spells, you should speak to your doctor or another medical professional for guidance.


¹ Richter, J. Sebastian, et al. “A Systematic Review of the Complex Effects of Cannabinoids on Cerebral and Peripheral Circulation in Animal Models.” Frontiers in Physiology, vol. 9, 29 May 2018, 10.3389/fphys.2018.00622. Accessed 6 Jan. 2022.

² Ramanlal, Riddhi, and Vikas Gupta. “Physiology, Vasodilation.” PubMed, StatPearls Publishing, 2020, www.ncbi.nlm.nih.gov/books/NBK557562/#:~:text=Vasodilation%20is%20the%20widening%20of.

³ ​​Mayo Foundation for Medical Education and Research. “Low Blood Pressure (Hypotension) - Symptoms and Causes.” Mayo Clinic, 14 May 2022, www.mayoclinic.org/diseases-conditions/low-blood-pressure/symptoms-causes/syc-20355465.

⁴ Mathew, Roy J., et al. “Postural Syncope after Marijuana: A Transcranial Doppler Study of the Hemodynamics.” Pharmacology, Biochemistry, and Behavior, vol. 75, no. 2, 1 May 2003, pp.

⁵ “Heart Health | Health Effects | Marijuana | CDC.” Www.cdc.gov, 10 Sept. 2021, www.cdc.gov/marijuana/health-effects/heart-health.html.

⁶ Abuse, National Institute on Drug. “Cannabis (Marijuana) Concentrates DrugFacts.” National Institute on Drug Abuse, 25 June 2020, nida.nih.gov/publications/drugfacts/cannabis-marijuana-concentrates.

⁷ Mathew, R. J., et al. “Middle Cerebral Artery Velocity during Upright Posture after Marijuana Smoking.” Acta Psychiatrica Scandinavica, vol. 86, no. 2, Aug. 1992, pp. 173–178, 10.1111/j.1600-0447.1992.tb03247.x. Accessed 2 Dec. 2021.

⁸ Gilbert, Christopher R, et al. ““Smoking Wet”: Respiratory Failure Related to Smoking Tainted Marijuana Cigarettes.” Texas Heart Institute Journal, vol. 40, no. 1, 2013, pp. 64–7, www.ncbi.nlm.nih.gov/pmc/articles/PMC3568288/.

⁹ Havenon, Adam de, et al. “The Secret “Spice”: An Undetectable Toxic Cause of Seizure.” The Neurohospitalist, vol. 1, no. 4, 9 Sept. 2011, pp. 182–186, 10.1177/1941874411417977.

¹⁰ www.ncbi.nlm.nih.gov/pmc/articles/PMC6312155/&sa=D&source=docs&ust=1671261057744732&usg=AOvVaw0PjQtucQ1J14y2XtTTWx8c. Accessed 17 Dec. 2022.

The information in this article and any included images or charts are for educational purposes only. This information is neither a substitute for, nor does it replace, professional legal advice or medical advice, diagnosis, or treatment. If you have any concerns or questions about laws, regulations, or your health, you should always consult with an attorney, physician or other licensed professional.

Continue Reading:

You might also like: