Anyone with even a passing experience with weed knows that the eyes can tell a story.
Bloodshot eyes? Someone’s probably been smoking up. Dilated pupils? Another strong indication they’ve just recently put down the bowl or joint.
But what about drooping eyelids?
Someone’s eyes “getting low” after using cannabis isn’t as common as red eyes or dilated pupils, but it’s certainly not unheard of.
What causes that to happen? For that matter, what causes some weed smokers to develop bloodshot eyes or dilated pupils?
Let’s get out our ophthalmoscope to examine the subject of weed and its effect on the eyes.
What Makes Eyes Look “Unnatural?”
Bloodshot eyes or big pupils aren’t evidence that would stand up in court — at least, not to definitively prove that someone’s been using cannabis. The same is true for drooping eyelids.
1. Red Eyes
Red eyes might also be a sign of alcohol or coke use. They could be caused by a number of other problems like allergies, conjunctivitis, eye injuries, or even keeping contact lenses in too long.
2. Dilated Pupils
Dilated pupils (known to doctors as anisocoria) can be the result of using coke, meth, ecstasy, or acid, eye injuries, or serious medical problems. They can also be caused by some medications, low levels of light, or simply an eye test at your doctor’s office.
3. Low Eyes
“Low eyes” can be a medical issue present at birth or developed later in life as the skin and muscles around the eyes weaken. The problem can also occur after cataracts or LASIK surgery, or as the result of a tumor.
The problem of drooping eyelids is called ptosis, and it can sometimes be treated with surgery.
Quite often, though, all of those unnatural-looking eye conditions, including “low eyes,” really are signs of having used cannabis.
What’s the connection? (Hint: It’s not due to irritation from weed smoke.)
The Body’s Endocannabinoid System
Before we talk specifically about eyes, we have to briefly discuss how cannabis interacts with the body.
An enormous number of the body’s functions are regulated by its endocannabinoid system (ECS). It’s composed of receptors located throughout the body, which receive signals from chemical neurotransmitters produced internally. Those neurotransmitters are called endocannabinoids.
Cannabinoids in weed-like THC and CBD have a molecular structure extremely similar to that of endocannabinoids. So when you smoke or ingest cannabis, its THC is able to interact with ECS receptors in the body and brain.
That’s how weed produces its trademark psychoactive effects and provides its medical benefits. THC can block naturally-occurring endocannabinoid system function, or send its own signals through the ECS.
There are lots of ECS receptors in the body, many of them in and around the eyes. In other words, it makes complete sense that smoking weed might cause the eyes to do unusual things.
We now return you to our regularly-scheduled discussion of low eyes, red eyes, and drooping eyelids.
“Low Eyes” and Weed
We’ll start with the one that’s hardest to explain.
It’s quite possible that you’ve never experienced drooping eyelids after smoking up, and that you don’t know anyone who has. It does happen to many people, though, and a few even users experience shaking eyelids.
The reasons, unfortunately, aren’t clear. A meta-review of the literature found only 20 studies that have been done on weed’s effects on eyelids. Almost one-third of them didn’t focus on pot causing problems at all; they studied the potential use of cannabis to treat a syndrome called blepharospasm, or uncontrolled eye twitching. Those studies don’t help us.
The rest of the research was more to the point.
Three studies considered police reports on drivers who had been stopped for suspected marijuana intoxication; the drivers all showed eye twitches, which were considered a sign of impairment.
Research suggests that cannabis might have the activated TRPA1 receptors that cause dry eye syndrome, which in turn caused the twitches. Those receptors aren’t technically part of the ECS, but cannabinoids do interact with them. That’s just a theory, though.
The rest of the studies focused on drooping eyelids, or “low eyes,” but they were all done with animal subjects, not human participants.
The most important takeaway deals with ptosis, the medical term for drooping eyelids we talked about earlier. It’s apparently caused by signals from the endocannabinoid anandamide — meaning that the ECS is involved in causing eyelids to droop. And that means that THC could interact with the ECS to cause “low eyes” as well.
Why wouldn’t it happen to every weed smoker? There’s no firm explanation, but ptosis is an inherited condition. So it’s possible that tokers whose eyelids droop after enjoying the green may have a family history of the condition. It’s also quite possible that stronger weed is more likely to cause low eyes.
That’s the best explanation. There are two other theories though. One speculates that when people get totally wasted, their eye muscles relax so much that their eyelids sag; there’s one study that linked high THC content with a greater occurrence of ptosis. The other theory is that the ECS might trigger eyelid drooping during severe cannabis withdrawal.
Short version: experts aren’t sure why your eyes might get low when you smoke weed — but you’re not wrong to think that there’s a connection.
Bloodshot Eyes, Dilated Pupils, and Weed
The red eyes and dilated pupils associated with weed smoking can be explained much more easily.
THC is a vasodilator, meaning it causes blood vessels and capillaries in the body to expand. That effect is caused by THC’s interaction with ECS receptors.
There are numerous receptors in and around the eyes, and numerous capillaries located behind the whites of the eyes. When THC hits those receptors, more blood flows through the expanded capillaries — causing the whites of the eyes to look red. Voila! Bloodshot eyes.
Two things might explain dilated (larger than usual) pupils. One is that when capillaries expand, pupils expand as well. The other is that smoking up produces a release of dopamine (the “feel-good” hormone), and studies show that higher levels of dopamine can cause pupils to dilate.
That’s not a universal reaction, though. Some peoples’ pupils actually get smaller when they toke up. Many people’s pupils aren’t affected at all. Not everyone gets bloodshot eyes after consuming cannabis, either.
In other words, everyone’s body is different, so they have different reactions to weed. That may be due to heredity, THC tolerance, or the strength of the flower. The best advice is to celebrate our differences, accept the effects that weed may have on your eyes — and be sure to carry some Visine with you when you’re headed out to party.
Why Do Your Eyes Get Low When You Smoke Weed? FAQ
Q: Is there anything you can do to prevent low eyes when you smoke?
A: You could quit smoking, but that’s probably not a realistic answer. There isn’t much else you can do, but choosing a strain with lower-THC content might help. Some research associates higher THC consumption with a greater chance of “the eyes telling the story.”
Q: Would eye surgery help?
A: Only if you already have an existing ptosis problem. It’s one of the common medical approaches to drooping eyelids, but doctors aren’t going to recommend it simply because your eyes get low when you indulge.
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