Red eyes are typically a classic, telltale giveaway that someone has smoked weed.
For certain individuals, it is a guaranteed occurrence, while for others who seem to be less sensitive, red eyes may come and go depending on the quantity or quality of the cannabis they consume.
Lower blood pressure and dilated capillaries
After consuming a cannabis-based product (flower, concentrate, edible, etc.), users generally experience an increase in heart rate and blood pressure. This effect is due to the plant’s cannabinoids, which are chemical compounds responsible for some of the therapeutic and medicinal benefits of cannabis, and their initial interaction with the body. This rise in blood pressure and heart rate is comparable to normal physical activities like exercise or sex.
It generally takes about five to ten minutes for users’ heart rates to return to normal and for blood pressure to begin to decrease. As the blood pressure lowers, the blood vessels and capillaries dilate, including the ocular capillaries. The dilation of ocular capillaries causes increased blood flow to the eyes, which results in your eyes turning red and also reduces intraocular pressure.
In fact, according to Dr. Melanie Bone, a board-certified OB-GYN who practices in West Palm Beach, Florida, “It’s cannabis’ ability to reduce intraocular pressure in the eyes that makes it a potentially viable treatment for glaucoma, a group of eye disorders that causes damage to the optic nerves which can eventually lead to blindness. It also happens to explain why your eyes become bloodshot after smoking cannabis.”
Evidence that the THC found in cannabis can lower intraocular pressure (IOP) is a major reason why many glaucoma patients have attempted to use medical marijuana to treat and relieve symptoms of the disease.
How do different cannabinoids affect eye redness?
The eye-reddening effects of cannabis are tied directly to THC consumption. It is THC that causes increased blood pressure and heart rate, and the subsequent expansion of ocular blood vessels. In practical terms, that means that the more THC you consume, the redder your eyes will become.
As users build a tolerance to THC, though, they may notice a significant decrease in eye redness. In the same way that frequent cannabis consumption will eventually decrease the strength of intoxication, regular pot users experience less fluctuation in blood pressure and heart rate, and in turn lower levels of capillary dilation.
Likewise, cannabis users who prefer CBD, CBG, or CBN-dominant strains will experience significantly less eye redness than THC consumers. Unlike the immediate rush of THC, CBD, CBG, and CBN have far less psychoactive effects, and can even decrease blood pressure, eliminating the cardiovascular reaction and eventual red eyes of traditional, full-strength THC cannabis.
This explanation accounts for why red eyes can still occur even with the lack of smoke, such as when eating edibles. It is not the smoke that makes your eyes red, but the cannabinoids.
That being said, it is possible for some to have an allergy or irritation to cannabis or to smoke in general, and have increased redness of the eyes for this reason. However, for these sensitive individuals, the experience would likely be a universal reaction to smoke, be it cannabis, tobacco, or perhaps even incense.
How else can weed affect your eyes?
Normally, our pupils dilate in response to changing light; as it gets darker, our pupils get larger. But they expand in size for other reasons as well, including when we are sexually aroused and when we are performing complex cognitive tasks. But it is also known that certain drugs can cause pupils to get larger.
Pupil dilation, which is also referred to as mydriasis, happens when one of two muscle groups become activated, namely the iris sphincter and the iris dilator. The sphincter response is triggered by the parasympathetic nervous system (what regulates our autonomic bodily processes when we are at rest), and the dilator by the sympathetic nervous symptom (what controls physiological responses requiring a quick response such as fight-or-flight).
For example, drugs like MDMA, ecstasy, cocaine, amphetamines, and some antidepressants (like SSRIs) can increase serotonin levels in the brain which is a crucial neurotransmitter that regulates mood, including feelings of happiness and well-being. Serotonin agonizes the 5-HT2A receptors in the brain, which has the downstream effect of triggering the mydriasis response.
Drugs that trigger the release of dopamine, a related neurotransmitter, can also induce mydriasis. Marijuana is a good example. Dopamine cause pupils to dilate by exciting the adrenergic receptors, which in turn increases adrenaline (which the autonomic nervous system is sensitive to).
How to get rid of red eyes
The cause for red eyes from cannabis is a harmless, even possibly beneficial one, but that does not necessarily make it a welcome reaction to all. There are a few simple steps one can take to minimize or reduce the redness of eyes during or after smoking.
- Opt for low or no THC strains. Strains high in CBD may be a desirable alternative for those looking to lessen red eyes when toking.
- Have eye drops on hand, especially brands specially formulated to reduce eye redness.
- Stay hydrated by drinking plenty of water. Increasing your fluid intake may help alleviate the dryness you experience.
- Simply wait it out. Your eyes will only stay red for a few hours so just play it cool and wait it out.
- Wear sunglasses. This not only covers your eyes from people to see but could also make you look rather cool.