Why Does Weed Make Your Eyes Red: The Different Reasons

red eyes from smoking weed

Altered coordination, delayed response time, increased heart rate, and dry mouth are some tell-tale signs a person has just used weed. In today’s post, however, our focus is on red or bloodshot eyes. 

You’re probably wondering – why does weed make your eyes red? Some might assume that it’s because of the smoke entering the eyes.


There’s a scientific explanation for eye redness when smoking weed, which is what we’ll be talking about. More so, we’ll also discuss whether it’s dangerous or not. 

The Science Behind Red Eyes 

Whether you’re taking recreational or medical marijuana, at the heart of the enigmatic red-eye phenomenon lies the intricate relationship between cannabinoids and the human body’s endocannabinoid system. 

Tetrahydrocannabinol (THC), the primary psychoactive compound in marijuana, wields its influence by binding to cannabinoid receptors, triggering a cascade of effects. 

One such effect involves a process known as vasodilation or dilated blood vessels. This physiological response occurs when THC lowers blood pressure as it interacts with cannabinoid receptors present on the endothelial cells lining blood vessels. 

As these receptors are activated, the blood vessels relax and widen, allowing an increased volume of blood to flow through. In the context of ocular tissues, this surge in blood flow imparts a reddened appearance to the eyes.

As THC exerts its influence on cannabinoid receptors, the body’s natural balance is temporarily disrupted, leading to a visual manifestation of the physiological response. 

The redness in the eyes serves as a tangible reminder that the compounds within marijuana interact with our internal networks in complex and nuanced ways, leaving an unmistakable mark on the external canvas of our bodies.

Histamine Release and Inflammation

While vasodilation contributes significantly to the red-eye phenomenon, there’s more to the story than meets the eye. 

Another player is histamine—a chemical messenger that plays a pivotal role in inflammatory responses. 

When THC interacts with the body, it can trigger the release of histamines, setting off a chain reaction that results in localized inflammation. 

This inflammation affects the blood vessels in the eyes, making them more visible and causing them to appear reddened. Histamines, commonly associated with allergic reactions, contribute to the spectrum of responses that marijuana elicits within the body.

The Connection with Blood Pressure

When THC engages cannabinoid receptors, it has the potential to lower blood pressure.

THC lowers blood pressure temporarily, which can intensify the red-eye effect. 

As blood pressure decreases, the heart pumps blood with less force, allowing the vessels to relax and expand even further. This amplifies the flow of blood to the ocular tissues.

However, it’s important to note that the reduction in blood pressure caused by THC is often modest and transient. It’s not comparable to the clinical effect of medications specifically designed to lower blood pressure. 

For individuals with normal blood pressure, the drop induced by marijuana consumption is unlikely to pose significant health risks. 

But it’s a whole different story regarding changes in blood pressure if we talk about using a shatter. You may be wondering what is a shatter and the possible dangers of using one, so you might as well read our article about that. 

Dry Eyes and Irritation

Beyond biochemical interactions, the red-eye phenomenon also involves the delicate balance of ocular hydration. Marijuana’s impact on tear production plays a pivotal role in the emergence of red eyes. 

THC can lead to a reduction in tear production, causing the eyes to become dry. They are not only uncomfortable but also contribute to irritation and redness. 

When the eyes lack sufficient moisture, the conjunctiva—the thin, transparent layer covering the white part of the eye—can become more exposed and prone to irritation. 

This irritation, combined with the heightened blood flow from vasodilation, creates the perfect recipe for a distinctive red-eye appearance.

Impact on Intraocular Pressure

Delving deeper into the physiological intricacies, we encounter yet another facet of the red-eye phenomenon: the potential influence of marijuana on intraocular pressure. 

Intraocular pressure refers to the pressure within the eyeball, which is regulated by a delicate balance of fluid production and drainage. 

Marijuana, particularly its constituent cannabinoids, may lead to a temporary reduction in intraocular pressure. 

This reduction holds potential significance in glaucoma patients—a condition characterized by increased intraocular pressure that can lead to optic nerve damage and vision loss.

Is It Dangerous to Have Red Eyes from Smoking Weed?

Photo from Deposit Photos 

Red eyes after smoking marijuana are a common occurrence, whether it’s recreational or medical marijuana. But are bloodshot eyes harmful to health? 

Generally, they’re not dangerous. The redness happens because the blood vessels in your eyes get bigger when you consume marijuana. 

This is due to the compounds affecting your body’s systems, including THC. From increased blood flow to reduction of eye pressure, several factors can be culprits. It’s usually a short-lived effect and not a big concern for most people.

However, it’s important to be aware of your own health. If you already have heart problems, the changes in blood pressure caused by marijuana might be a bit risky. People who tend to have dry or irritated eyes might also find the redness uncomfortable.

What To Do When You Have Red Eyes from Smoking Marijuana 

If you find yourself with red eyes after smoking weed, don’t worry – there are simple steps you can take to manage this common occurrence:

Stay Hydrated

Drinking water is not only essential for your overall health but also for maintaining the health of your eyes. Adequate hydration helps prevent dryness, which can contribute to red eyes. 

When you’re well-hydrated, your eyes are less likely to feel dry and irritated, reducing the likelihood of redness. 

Use Eye Drops

Lubricating eye drops are your allies when it comes to managing red eyes caused by smoking weed. 

Over-the-counter eye drops can provide quick relief for dryness and irritation, soothing your eyes and minimizing redness. 

Look for ones specially formulated to combat redness, as these can be particularly effective in reducing the appearance of red eyes. 

Keep a bottle of these drops handy for those moments when your eyes could use some extra moisture and comfort.

Avoid Rubbing

When your eyes feel dry or itchy, it’s a natural impulse to want to rub them. However, rubbing your eyes can worsen the situation and lead to increased redness. 

The friction caused by rubbing can further irritate your eyes, intensifying the red appearance. 

Instead of rubbing, try blinking more often to help spread your natural tears or use lubricating eye drops to relieve discomfort without exacerbating redness.

Limit Usage

If you’re concerned about the red-eye effect, you might consider adjusting your marijuana consumption. 

Exploring different consumption methods can provide an enjoyable experience while minimizing the potential for redness. 


Photo from Deposit Photos 

In this article, we talked about why does weed make your eyes red. It isn’t the reaction from the harsh smoke. Rather, it’s a more scientific phenomenon, which has something to do with how THC makes your body react. 

Eye redness is a result of a combination of factors, such as lower blood pressure that makes blood vessels begin dilating. It also leads to increased blood flow in the eyes. More so, it can also be a reaction to histamines. 


How can you get rid of red eyes from being high? 

Being high on weed makes your eyes red, but there are ways to minimize the effects. For instance, you can apply redness-reducing eye drops or cold compress. 

How long do red eyes last? 

Eye redness from smoking cannabis can last one to four hours. This can depend on several factors, including the THC content in marijuana. 

Can eating edibles make your eyes red? 

Yes, eating edibles can also make your eyes red. This is especially true if you eat edibles that contain THC. 

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