What Are the Side Effects of Cannabis?

In general, most people tolerate cannabis well, especially when taken in a controlled way for medicinal purposes. But like any medical or recreational substance, there are some common side effects, the extent of which can differ from person to person depending on pre-existing conditions or interactions with other medications.

Some may experience adverse reactions at low doses, while others who are more tolerant may experience these only after consuming cannabis with a high level of tetrahydrocannabinol (THC), or after consuming large doses.

Regardless, it’s a good idea to be aware of the potential side effects, and to take protective measures — such as consuming cannabis in a safe environment or with a group of trusted friends — in order to avoid negative experiences.

Common Cannabis Side Effects

Cannabis contains many cannabinoids, but it’s THC — the main psychoactive ingredient — that is often responsible for triggering unwanted reactions. For many people, these are more common after consuming cannabis edibles, since it takes longer for the initial effects to be felt (“I’m not feeling anything yet,” is often the prelude to overconsumption of edibles, with predictable consequences).

Here are some of the most common side effects associated with cannabis use:

Anxiety and Paranoia:
Small doses of cannabis are commonly taken for medical purposes to help with anxiety. However, in larger doses, it can actually increase anxiety and paranoia.

How can it do both? It’s because of THC’s biphasic presentation — meaning it has two opposite effects at different doses. This is why mild THC strains in low doses are calming, but at high doses they can have make you feel paranoid.

Science has also shown that due to differing brain chemistry, some people have a genetic predisposition to anxiety which can magnify this side effect. CBD strains have been found to counteract the effects of THC — so it may be worth keeping some on hand to help you relax from a paranoid or anxious high.

Drowsiness, Insomnia, and Lethargy:
THC has the therapeutic ability to relieve insomnia by helping you relax and fall asleep. But this is less useful if you want to stay alert and active, especially during the daytime.

If that’s your goal, it’s worth asking the professionals at your local dispensary for advice on strains. They may recommend one with a high CBD-to-THC ratio, which typically enables you to get through the afternoon without the need for an impromptu nap.

To avoid daytime drowsiness, it’s also helpful to choose sativa strains over indica. Indica has more of a sedative effect that can, at the very least, leave you feeling lethargic and lazy.

Increased Appetite:
THC is a known appetite stimulant, which is fine if you’re looking to gain weight. But if you don’t want the munchies, look for cannabis strains with higher ratios of THCV (tetrahydrocannabivarin). Studies have confirmed that this cannabinoid is an appetite suppressant — an effect that is also shared by CBD.

Bloodshot Eyes:
This is one of the most common side effects of cannabis use, and experienced users have long used eye drops to prevent redness and dryness. It affects everyone differently: some people experience severe discomfort every time they use cannabis, others get it mildly or not at all. It depends on the person, the strain, and the amount consumed.

This effect is caused by the dilation of capillaries in the eyes. Since THC lowers your blood pressure, this increases the amount of blood that reaches the eyes, and in turn reduces pressure within them. Ironically, this is also the reason people use cannabis to help treat glaucoma.

Increased Heart Rate:
While THC lowers blood pressure, it can also cause a rapid, increased heart rate for up to three hours after consumption. This can cause people to feel weak and dizzy — it can even be serious enough to cause a heart attack. If you have a diagnosed irregular heartbeat or coronary condition, be sure to discuss your cannabis consumption with your doctor.

Memory Impairment:
Not being able to remember recent events, particularly under the influence of cannabis, is a common cultural trope. However, studies have found that memory impairment is short-lived — lasting only 2-3 hours after consuming cannabis. This doesn’t impact existing memories, and has no long-term impact after a few days. One study also reports that people who frequently use cannabis can even build up a tolerance to impaired memory and recall.

Dry Mouth:
Commonly known as “cottonmouth,” high-THC cannabis can cause the mouth to dry up because of its similarity to anandamide — a natural chemical in the body that decreases the production of saliva by binding to receptors in our salivary glands.