Vasodilation In Cannabis Explained

Ever wondered why your eyes get bloodshot red after burning one? This is why...
03 December 2020
6 min read
Vasodilation In Cannabis Explained

  • 1. What is vasodilation?
  • 2. What's the link between marijuana and vasodilation?
  • 3. The reason behind the puffy red eyes
  • 4. Can you stop vasodilation?
  • 4. a. How to hide puffy red eyes
  • 5. Side effects of vasodilation
  • 6. The bottom line

Anyone who's ever smoked weed, regularly or not, has noticed the typical symptoms of a cannabis high. These signs are already well-known, we see them being exaggerated in paintings, movies, and TV series all the time. 

From a dry mouth, known as cottonmouth, to feeling giggly, the side effects of consuming marijuana can be quite evident. However, there is one special reaction to smoking cannabis which is the biggest tell-tale sign that a person is under the effects.

"The eyes can speak louder than words."

Never has a saying made more sense, the most evident demonstration that a person is high on weed is in their eyes, their puffy, bloodshot red, baked eyes. 

What's the reason behind the puffy red eyes caused by marijuana consumption? It's due to a phenomenon called vasodilation. Let's find out what vasodilation is and what are its effects.

1. What Is Vasodilation?

Vasodilation isn't a mechanism exclusive of cannabis consumption, but it happens indeed when you use the substance. 


Vasodilation illustrative image.

Vasodilation illustrative image.

In medical terms, vasodilation is what takes place when smooth muscles situated in the walls of our arteries or larger veins relax, resulting in the widening, or dilation, of the blood vessels.

This opening of the blood vessels leads to faster blood flow through the veins, and a decrease in blood pressure as well. Some substances and food sources that cause vasodilation include:


Nitric oxideBeets, garlic, dark chocolate, leafy greens, meat, nuts and seeds, citrus fruits, and more. 
Carbon dioxideThe atmosphere. 
AcetylcholineBeef, egg, soybeans, fish, quinoa, milk, vanilla yogurt, broccoli, brussels sprouts, and more. 
ProstaglandinsBananas, sunflower seeds, ginger, pineapple, 
HistamineAlcohol, bananas, tomato, wheat germ, papaya, chocolate, beans, citrus fruits nuts, and more. 

2. What's The Link Between Marijuana and Vasodilation?

The famous cannabinoid present in weed buds, THC, or tetrahydrocannabinol, is known to mimic the effects of anandamide. Anandamide is a fatty acid neurotransmitter that participates in the regulation of pain, appetite and fertility, and the neural generation of motivation and pleasure.1

Just like most of marijuana's cannabinoids, this anandamide lipid mediator is synthesized by the CB1 receptors in the endocannabinoid, taking part in memory management, higher thought processes, and movement control.


Anandamide, and therefore also THC which mimics this fatty acid, is a vasodilation promoter, decreasing blood pressure and the heart rate. But how exactly is it that blood pressure lowers as blood vessels widen? 

Well, it makes sense. Imagine if you had a hosepipe with running water. When you put pressure on the edge, making the hole smaller, the water runs typically faster, coming out with more pressure. This would be the high blood pressure state in our veins, running at a fast pace


Puffy red eyes are caused by the vasodilation effect of marijuana.

Puffy red eyes are caused by the vasodilation effect of marijuana.

When you let go of the hose's edge, letting the hole go back to its previous form, water won't be running as powerfully as before. This would make the state of vasodilation in our veins when they are under the effects of marijuana. 

Blood pressure lowers because the volume is inversely proportional to pressure, as the 'hose' or veins widen, the volume of liquid that can be held in the 'tube' increases too, so the water or blood pressure is dropped.

3. The Reason Behind The Puffy Red Eyes

Anyone can experience red eyes for many different reasons, and smoking marijuana could well be one of those. Puffy red eyes are a natural reaction of our bodies' cardiovascular system under the influence of THC. 

When a person smokes, vapes, or eats cannabis edibles a two-step process takes place. Right after the substances have reached the endocannabinoid system, a short increase in the heart rate and blood pressure takes place, which is the opposite process of vasodilation, known as vasoconstriction. 


The reason behind puffy eyes is the body's reaction to THC.

The reason behind puffy eyes is the body's reaction to THC.

Briefly after, the exact opposite happens, the heart rate drops, and our veins expand, or vasodilate. Through the vasodilation of our blood vessels and capillaries, as we mentioned, the tiny muscles around the veins relax, allowing blood to travel through more freely.

Since our eyes are structured with big amounts of small blood vessels, as they expand they become more visible, turning our eyes bloodshot red, making the fact that you're high on weed unmaskable. 

4. Can You Stop Vasodilation?

If you still need to mask the fact that you are a marijuana user then what you are most likely wondering is if you can prevent vasodilation from happening.

In the first instance, the answer would be no, you can't stop vasodilation from occurring when you consume cannabis. This is because vasodilation is a mechanism that takes place at a subconscious level, therefore we have no capacity to control either the vasodilation or vasoconstriction processes. 

How To Hide Puffy Red Eyes

Given vasodilation is an autonomous process we can't precisely prevent, what we can actually do is find remedies for it. There are in fact a couple of known remedies that work effectively in getting rid of red, bloodshot eyes, such as: 

  • Using allergy eye drops;
  • Using artificial teardrops;
  • Chucking on a couple of sunglasses.

When it comes to eye drops, you have two options: allergy drops and artificial tears. The first is more efficient in handling eye redness, given it has a complex chemical structure focused mainly on alleviating the symptoms of allergies, which include eye discomfort, itchiness, and redness. 

Artificial teardrops, on the other hand, aren't as effective as allergy eye drops but they can help too. These drops are easy to get, you can purchase them as an over-the-counter medication at the nearest pharmacy. Originally they are intended to treat eye dryness, but they can aid with the redness too. 


Use allerdy drops or artificial tears and relieve eye redness fast.

Use allergy drops or artificial tears and relieve eye redness fast.

Between allergy drops and artificial tears, the first one isn't too recommended for regular use since they can harm your vision in the long run, so if you know you're going to give a strong use to these red-eyes remedy then we suggest you should rather use the artificial teardrops. 

Lastly, if you're not much into using eye drops, then perhaps the easiest go-to solution for hiding your bloodshot eyes are sunglasses. It's easy, simple, and fast, chuck your glasses on and relax in your high.

However, take note that these are only daytime alternatives unless you want to be that guy wearing glasses at night, and ruin your eyesight while you're at it. 

5. Side Effects Of Vasodilation

The effects of vasodilation in the body can be both healthy and bad for you, depending on the vasodilation levels and each person's health condition. For example, as a vasodilator, cannabis' THC is also known for relieving headaches and migraines.2

If your myth-buster alarm just went off, we get it, and we're impressed with your knowledge. It wouldn't make that much sense to state that a lowered blood pressure could relieve a headache since slow blood flow in the brain causes a decreased neural aerobic respiration, which is a normal cause of headaches


Vasodilation from cannabis can ease blood pressure and slow the heartrate.

Vasodilation from cannabis can ease blood pressure and slow the heart rate.

Nevertheless, before you bust this myth, you should keep in mind that one of the main activities of THC is acting upon the endocannabinoid system's receptors, which, among other duties, are in charge of pleasure

This way, the effects of THC binding with the CB1 receptors end up outweighing the slightly reduced blood flow and achieving therefore to counteract migraines and headaches

Since one of the main effects of vasodilation is decreasing blood pressure, cannabis could be promising for treating cardiovascular disorders, such as stroke, atherosclerosis, restenosis, MI, and heart failure. However, more research yet needs to be done on this aspect.3

6. The Bottom Line

If you've ever noticed your eyes were red like hell after you smoked a joint or hit your bong, there is nothing you should worry about. In fact, exhale with ease, because this means your body is running smoothly

Puffy red eyes are meant to happen when you use cannabis, therefore when you don't experience this is when you should get worried. 

For now, enjoy your baked face and learn how to mask your red eyes from those who aren't supposed to notice you are higher than the clouds. 



This content is for educational purposes only. The information provided is derived from research gathered from external sources.



  1. "The effects of Δ9-tetrahydrocannabinol in rat mesenteric vasculature, and its interactions with the endocannabinoid anandamide" Saoirse E. O'Sullivan, David A. Kendall, and Michael D. Randall. June 2005.
  2. "The Use of Cannabis for Headache Disorders" Bryson C. Lochte, Alexander Beletsky, Nebiyou K. Samuel, and Igor Grant. April 2017.
  3. "Role of cannabis in cardiovascular disorders" Hemant Goyal, Hamza H. Awad, and Jalal K. Ghali. July 2017. 
03 December 2020