Possible Side Effects and Drug Interactions

Side effects are possible with cannabis use. The severity of symptoms can range from very mild to very intense depending on a variety of factors. It should be noted that there is no lethal dose of cannabis, and severe side effects are very rare. The majority of side effects that can occur will cause patient discomfort for a relatively short period of time and then pass. The response to medical cannabis and potential severity of side effects can vary widely from patient to patient. To mitigate potential side effects the motto "start low and go slow" should be used. You can always increase your dose of cannabis, but once taken, you can't "take it away". Side effects can range from dry eyes, dry mouth, dizziness, drowsiness, increased heart rate, decreased blood pressure, decreased blood sugar,  lack of balance, increased appetite, decreased motor function, decreased cognitive abilities, and short term memory loss  to panic attacks and exacerbations of psychosis symptoms.


It should be noted that many of the "more severe" side effects occur in patients that ingest high dose edible products. This is because the liver converts delta-9-tetrahydrocannabinol (what we call THC) to 11-hydroxy-delta-9-tetrahydrocannabinol. This 11-hydroxy-THC is estimated to be between 3-10x more potent than THC, which explains the increased potential for side effects with edible products.

When using edible products, start with a dose of 2.5-5mg and wait at least 2 hours before taking any additional dose. If ineffective, you can increase your initial dose next time. However, it is not recommended to increase your initial dose by greater than 2.5-5mg each time. In slowly "working up" your initial dose, you can find the lowest dose that is effective, while decreasing your chances of experiencing severe side effects.


If you are currently taking prescription drugs or supplements you should discuss cannabis use with your physician and/or pharmacist. There are potential drug interactions possible with a variety of pharmaceuticals when combined with cannabis. To assess the possibility of potential drug interactions, your doctor or pharmacist will need to know that THC is metabolized by CYP3A4 and CYP2C9, and CBD is metabolized by CYP3A4, CYP2C9, and CYP2C19. Pharmaceuticals that "inhibit" these systems can increase THC and CBD levels, while pharmaceuticals that "induce" these systems can decrease THC and CBD levels. It should also be noted that THC is a CYP1A2 inducer, and CBD is an inhibitor of CYP3A4 and CYP2D6.

Many classes of medications fall into these categories for potential interactions with cannabis.  Consuming cannabis while taking these medications is not contraindicated, however proper monitoring and potential dosage adjustment should be discussed and monitored by a physician. Examples of common drug classes that may have potential drug interactions is as follows (this list is not inclusive):




Antiviral drugs

Antidiabetic drugs



Antifungal drugs

Blood pressure and/or cholesterol drugs

If you are currently taking a medication that is designated as having a "narrow therapeutic index", it is even more critical that you tell  your physician about your medical cannabis use. These types of medications have an even higher chance of needing to be dose adjusted when used with cannabis. Examples are as follows (this list is not inclusive):


1. Phenobarbital, Carbamazepine, Valproic Acid and anti-convulsants in general

2. Warfarin or blood thinners in general

3. Digoxin

4. Lithium or other anti-psychotics and/or mood stabilizers in general

5. Cyclosporine or other immunosuppressive drugs in general

6. Levothyroxine or other thyroid medications in general

7. Theophylline