Side Effects

In this article, we explain the side effects of cannabis so new users know what to expect. There are no long-term side effects, only short-term side effects while THC is in the system.

The side effects of cannabis are dependent on how it is consumed. Oral cannabis products, like edibles or tinctures, have a slower onset of action and the THC is absorbed slowly. This causes the side effects to be less. When THC is absorbed into the system rapidly, like inhalation, the side effects are more intense. The rate that THC enters into the body makes a big difference. If you puff on a vape pen over a ten to twenty minute period, you will have a more comfortable onset of medical benefit than if you smoke the same amount of THC in rapid succession, or vaporize it in concentrated form in one inhalation.

Don’t be afraid of these side effects. Know that they can occur and some are common, but the medical benefits outweigh the side effects. Some of the severe ones listed below are very rare and can be prevented by purchasing products from dispensaries and using small amounts at a time. Don’t overdo it.

The High

The psychoactivity and “euphoria” of cannabis is called the high. It is very difficult to explain in words the way it feels. Also, it changes over time. The high of someone using it the first time is much more intense and feels very different from the high of someone who uses cannabis every day for decades. Tolerance makes a big difference in how someone’s high feels. There are components to the psychoactivity of cannabis that go away and never come back once a tolerance is developed. One of the wonderful things about cannabis is that the medical benefits stay even after the side effects go away.

The first time patients use cannabis it feels like a trip. It is completely unlike alcohol. There can be a vague feeling of repeating deja vu. This is because the active ingredient THC is fat-soluble and deposits in the fatty white matter tracts of the brain that connect various anatomical parts of our brain. The largest white matter tract in the brain is the corpus collosum, an enormous highway connecting both sides of our hemispheres. Somehow cannabis can create a feeling of deja vu when it deposits in the corpus collosum and disrupts its usual activity. There is a slight desynchronization between the two hemispheres. It can feel like reality is being seen through an antique projector with a low frame rate. There can also be visual trailing, a kind of hallucination.

The perception of time is warped. It can seem like time has slowed down sometimes and a short amount of time can feel like an eternity.

These bizarre side effects can be minimized by using only small amounts the first few times using cannabis (see article First Time Using Marijuana). Again, they are a phenomenon in the cannabis-naive person, someone who has never used it prior to trying it. They are not present in people who are familiar with the effects. Once someone has used cannabis on a regular basis, their high becomes a vague background affect that does not interfere with their daily experiences, but the users should prepare to take the rest of the day off when they try cannabis for the first time.

Sensory Side Effects

Marijuana causes changes in the sensory perceptions of users. As mentioned above, there can be visual trails in the visual perception of new users. Colors can appear more vibrant and the appearance and appreciation of art can be vivid. Using cannabis before entering an art museum can be a wonderful experience.

The sound of music is enhanced. Not only is the rhythm more stimulating but the timbre of the instruments is perceived to be more enjoyable. There is an improved sensitivity to the nuances that make a song special. It is not that the sound is louder, but that the details of the song are more salient.

Tactile sensation is also more sensitive. While pain may go away or subside, the skin becomes more able to feel touch. When we put on a shirt, we can feel it as it is put on, but for the rest of the day we don’t feel it anymore. Using cannabis can bring out some of these suppressed and desensitized sensory inputs. It can be especially well perceived to feel another person’s skin on your own. Marijuana can improve romantic moments in this way and even increase libido.

Food tastes better. The “munchies” are a classic side effect that result in a strong desire to eat food. The flavors will be more pleasurable. Some patients worry that cannabis use will make them gain weight from this but in actuality it seems to cause patients to lose weight (another article on this here). Probably this has something to do with long-term appetite suppression despite short-term munchies.


Cannabis can have a real effect on the psychology of a person. Unlike alcohol, which is a disinhibitor and causes people to do stupid things they regret, cannabis is more of an inhibiting drug that makes people more perceptive to how they may appear and behave. This can make people more introverted and self-reflective. There is often a stronger internal dialogue when a person is high that leads to introspection, sometimes leading to a lot of self-criticism. As a society, we worry about patients using cannabis before driving (and it is not recommended for most people) but a high driver will be more inclined to think to themselves that they are driving too fast and reckless, even when they are the slowest one on the road with both hands on the wheel staring directly ahead.

Short-term memory is affected. It will be easy to forget where you put your keys or someone’s name after just meeting them. Absolutely refrain from using cannabis before a difficult exam. It will be hard to remember things and answer correctly. This may be due to the increased awareness of the surroundings and sensory stimulation interfering with memory recall than an actual amnesia of some kind.

There can be a discomfort in unfamiliar surroundings, especially in social situations since cannabis makes some people more introverted and even socially awkward. On the other hand, it can be used in patients for social anxiety to help them socialize too. But for the most part it does tend to make people more introverted when they are new to cannabis. There can also be some paranoia and anxiety caused by cannabis. For this reason, we recommend trying marijuana the first few times at home or in a familiar environment with people you are comfortable with.

The first several times using cannabis can cause people to have a lot of laughter, almost to the point of histerical giggles. This is a fun side effect of the drug that unfortunately, like the others, goes away after a while.

After using cannabis, it is very easy to fall asleep. In fact, it can cause people to become very sleepy, especially if they have been sleep deprived. Cannabis generally helps people stabilize their minds and bodies in many ways. If a person has been lacking sleep, cannabis will push them to a sleepy state and help them catch up on their rest. On the other hand, if someone has been over sleeping, cannabis can keep them awake sometimes too. It is not recommended to use cannabis immediately before going to sleep because there can be an excitatory effect on the individual that will cause them to stay awake. If you want to use cannabis for sleep, inhale it 1-2 hours before going to bed. By the end of your high, you will be ready for a good night’s rest.

Body Symptoms

Marijuana causes people to get red eyes. This is one of the most stereotypical side effects of cannabis. Everyone can imagine a stoner with red eyes. Counter this by using eye drops before you use cannabis to prevent them from getting red in the first place. You can also use them afterwards. It can make you feel more comfortable around others to use eye drops so you don’t look so obviously under the influence of cannabis. That way no one can tell you are high from your appearance.

Dry mouth, also called cotton mouth, can be very intense. Keep some hydrating liquids around to wet your lips and oral cavity. Chapstick can be useful too.

A very common side effect of using cannabis is heart palpitations. The heart will beat stronger after getting high. Patients with heart problems and the added paranoia from getting high may worry that they are having a heart attack. While it is true that smoking cannabis has been documented to cause an increase in heart attacks, this is very uncommon. It similar to the way going up a flight of stairs has an increased incidence of causing a heart attack too. When you feel heart palpitations, do not worry. This is a very common side effect. If it bothers you enough, consider asking your doctor for a prescription of low-dose propranolol (a beta blocker), which is relatively safe and prevents palpitations caused by marijuana.

When a large amount of THC is used, like with dabbing concentrates (see Vaporizing Concentrates), there can be a significant amount of sweating that occurs. In severe cases, patients can become nauseaus and even throw up, though this is only when a patient overdoses and uses too much THC. If you are new to cannabis and take a two-foot bong rip, you will overdose and possibly become nauseaus and throw up. Don’t do that. We recommend vaporizing from a vape pen with oil cartridges so you can better control how much you are inhaling and put it down before you over administer.

Panic Attacks

Rarely, when a patient uses too much cannabis they can have a panic attack. This usually happens because they get an intense paranoia that they used too much and may need medical assistance. Then they experience heart palpitations from the cannabis, which validates their fear that they are overdosing. Everyone gets worried when they feel their heart pounding in their chest. They may feel that they are having a heart attack.

At this point, the person tries to calm down and relax their body to slow their heart down. How do they do this? They focus their attention on their breathing. They try to breath slow, deep respirations. Often they will breath in through their nose, and out of their mouth. Society has seemed to tell us that this is a beneficial thing to do to relax. Unfortunately, this causes some effects in the body and since cannabis makes someone more perceptive to their sensory inputs and introspective, focusing on their internal state, they sense the changes from the breathing. One of the major things that happens is that patients begin to feel short of breath. Their hyperventilation from focusing on their breathing causes their blood vessels in their body to constrict (the body constricts blood vessels when there is plenty of oxygen and vasodilates when there is less oxygen so it can deliver more of it to the tissues). The constriction of their blood vessels causes them to feel like they are not catching their breath as well as they should with a deep breath. Because of this they begin to breath deeper which eventually causes them to get light headed from the lack of carbon dioxide in their blood. Now they really panic because they are spiralling out of control.

If you find yourself in a situation where you are having a panic attack like this, the best thing to do is reset your blood gasses. Stop hyperventilating and hold your breath for some time to let the carbon dioxide accumulate and build up in your blood vessels. Let your blood vessels in your body dilate from this breath hold. Now when you start breathing again, it feels like you are repleneshing your oxygen again. Then, stop focusing on your breathing and let your body breath on its own. It will balance itself. This concept has been explained in more detail in the book The Clinician’s Guide to Medical Cannabis.

Rare Conditions

There are some patients who are prone to schizophrenia. Cannabis does not cause schizophrenia but it has been documented to bring it out earlier than it would have otherwise in people who are prone to it. If you have a strong family history of schizophrenia or you are experiencing delusions or symptoms of it, it would be wise to hold off of cannabis use. It is very rare for cannabis to cause someone to have schizophrenia but it has been shown to happen in some individuals.

Chronic users who use very large amounts of THC have been seen to have a cannabis hyperemesis syndrome resulting in severe nausea and throwing up that is improved by hot showers. They will show up at emergency departments because their hot water ran out and they start vomitting again. This is easily treated by discontinuing use. Cannabis usually prevents and treats nausea so we don’t understand why this happens but if you are dabbing every day and start to experience nausea and vomitting that’s improved by hot showers, stop using cannabis immediately.

Finally, there were some scare reports of people getting lung damage from vaping cannabis. This e-cigarette vaporization associated lung injury (EVALI) condition also known as vaping-associated pulmonary injury (VAPI) was shown to be caused by vitamin E acetate in products bought off the street. This is more the reason to get a medical marijuana card and have access to state-approved lab-tested cannabis products from your local dispensary.

Further Reading

Make sure to check out our Cannabis Education section for other articles about cannabis.
Also, if you are a physician or healthcare provider it would be very wise to read The Clinician’s Guide to Medical Cannabis, which is a superb resource for learning about incorporating cannabis into your healthcare practices.