The HERB Blog


Why Does Weed Cause Red Eyes?


If you just finished off a pre-roll and are wondering why your eyes look bloodshot in the mirror, have no fear. Weed causes red eyes in some people, and it’s generally not a cause for concern. The effect is caused by the tetrahydrocannabinol (THC) in your bloodstream, and it typically doesn’t last for very long. But why does THC make your eyes red in the first place? The answer to that is a little more nuanced.

Why Does THC Make Your Eyes Red? 

Cannabis has been shown in studies to reduce intraocular pressure in the eye. Incidentally, this is why physicians sometimes recommend medical cannabis to glaucoma patients. However, this reaction is also a big part of why weed causes red eyes. 

When THC enters the bloodstream, it binds to the body’s natural cannabinoid receptors (CB1 and CB2). When this happens, your blood pressure drops, causing blood vessels and capillaries (including the capillaries in the eye) to dilate. This dilation results in an influx of blood flow to the eye, causing the visible redness that’s so familiar to cannabis connoisseurs. 

The blood pressure drop usually happens within 15 to 20 minutes of smoking cannabis flower, and the effects can last a couple of hours or more. Of course, other cannabis delivery systems can impact these numbers. For example, if you’re consuming cannabis edibles, the time frame for weed and red eyes is significantly different. Edible cannabis is processed through the digestive system and metabolized by the liver. As a result, the onset is slower and the effects last significantly longer in most cases.

Can You Prevent Getting Red Eyes From Cannabis? 

It’s understandable to want to be discreet when consuming cannabis—whether you’re consuming for medicinal or recreational reasons. The best way to avoid the red eye problem is to stick with low-THC strains. Some cannabis strains have THC concentrations north of 30%, although 15-20% is more typical. If you can find a lower strain in the 10-12% range, this may help to reduce the red-eye effect. Alternatively, you can opt for hemp-based CBD oil products when discretion is key. Even full-spectrum CBD products will contain no more than 0.3% if they’re hemp-derived, so you don’t have to worry about the red eye.

How Do You Reduce Visible Red Eyes from Cannabis? 

If you already have red eyes and are looking to conceal the issue, there are a few basic home remedies that may be able to help. For instance:

  • Stay hydrated as much as possible. Eye redness is linked to dehydration, and you can often mitigate the issue (at least in part) by drinking plenty of water. 
  • Apply moisturizing eye drops. Over-the-counter eye drops work by constricting the blood vessels that transfer blood to the eyes, which in turn can reduce visible redness. Look specifically for eye drops with lubricants and decongestants. 
  • Place ice packs over your eyes. Just be careful not to expose your eyelid directly to the ice.  
  • Wear sunglasses. When all else fails, you can always cover up the issue. This approach may raise some eyebrows if you’re indoors, but it can be useful as a last resort. 

Depending on your unique body chemistry and how much THC you’ve consumed, these techniques can vary in their results. If you’re unsuccessful, the best thing you can do is wait it out.

close-up of green cannabis leaves

Is Having Red Eyes From Cannabis Dangerous?

In most cases, the red-eye effect is just a natural bodily reaction to the cannabinoids at work. Within a few hours, your appearance should return to normal. However, it is important to watch out for other concurrent side effects like: 

  • Racing heart
  • Paranoia or hallucinations 
  • Anxiety or panic attacks 

In general, cannabis side effects should be mild. If they persist, consider cutting back or switching to a lower THC strain. If you experience more intense side effects, like severe nausea or vomiting, visit your doctor. These types of effects may be indicative of a rare condition called cannabis hyperemesis syndrome. 

How to Know if Weed Caused Your Red Eyes

Finally, it’s important to note that red, bloodshot eyes can have several causes beyond cannabis use. For example, eyestrain, inflamed blood vessels, and allergies are other common causes that may account for the issue. If you’re a regular cannabis consumer, it’s fairly easy to deduce whether your weed and red eyes are related or if there’s another cause to look into.

If your red eyes are cannabis-related, the effect should kick in within a few minutes of consumption and should subside within a few hours. You should naturally learn to predict when it will happen and approximately when the issue will subside. In addition, if your eyes burn, itch, or water excessively, there may be another condition at work. 

If you experience red or irritated eyes even when you aren’t consuming cannabis, or if your red eyes persist long after you’ve finished your smoke session, you may have another underlying issue that needs addressing. In that case, you should visit your eye doctor to learn more about what’s going on. Your doctor may be able to prescribe special eye drops to address allergies or general irritation. 

Don’t Let Red Eyes Ruin Your Experience 

Red eyes are typically just a mild side effect of consuming cannabis, and the “weed red eye” effect is generally nothing to worry about. If you need to be discreet about your consumption, why not choose a strain with low THC, so that it doesn’t make your eyes red? Just remember to time your consumption accordingly and take additional measures if necessary (like opting for low-THC strains and keeping a bottle of hydrating eye drops at hand at all times). 

And, of course, always know your limits. THC, like all things, is best consumed in moderation. So as long as you don’t constantly push the limits of your tolerance threshold, you should have an enjoyable experience with minimal side effects.