Cannabis by itself poses very little to no risk to most people. But that changes when you incorrectly use it, and one of the most dangerous mistakes you can make is mixing cannabis with certain medications by yourself. Why? Some medications become toxic when used alongside cannabis, while others may lose their effectiveness, leaving your condition untreated.
To help you avoid using marijuana dangerously, we’ve compiled a list of drugs you should never use alongside it on your own. Keep in mind that some might be combined only under medical supervision in special circumstances, but you should never adjust your own meds or start doing so on your own.
Here’s the list:
Blood thinners or anticoagulants help prevent blood clots from forming or growing larger. They’re typically prescribed to reduce the risk of strokes, heart attacks, and pulmonary embolisms caused by blood clots. However, mixing weed with blood thinners can be risky. That’s because THC and CBD, the two main cannabinoids (cannabis compounds), can interact with the same liver enzymes that process blood thinners and other medications.
These cannabinoids may slow down how quickly these enzymes break down blood thinners, leading to the medication staying in your system longer. This increases the medication’s effect, putting you at risk of easy bruising or uncontrolled bleeding. It may also amplify common side effects of anticoagulants, such as dizziness, drowsiness, or confusion.
Commonly prescribed anticoagulants include:
A systematic review suggests that heavy cannabis use may amplify warfarin’s anticoagulant effects. Another study supports this by showing that cannabis may slow warfarin’s metabolism, leading to delayed blood clotting. Cumulative data show that there are several case reports indicating higher warfarin levels in serum, higher INRs, and an increased risk of bleeding.
However, there is contradictory evidence from a case report where INR was not affected by daily cannabis use in an 85-year-old patient, indicating this is nuanced and not always straightforward. Also, recent research suggests that less than 30 mg of THC daily may not cause significant interactions here, but CBD might anyway.
Speaking to your specialist first is best for their opinion and making informed decisions together. They will need to monitor your labs and adjust your doses of warfarin (by ~22-31%), cannabis, or both. You should never adjust or stop medications like blood thinners by yourself.
Prescription and over-the-counter (OTC) sedatives can help you sleep longer and better, at least in the short term. Most of them work by slowing brain activity and helping you relax. Many cannabinoids and terpenes can also have sedative and deep-sleep-promoting effects to help you sleep. As such, combining cannabis with sleeping aids can enhance the effects of both substances, potentially leading to excessive drowsiness, confusion, and impaired coordination.
The real danger lies in how these combined effects can severely impact your ability to function safely. When cannabis and sedatives amplify each other, your risk of accidents, falls, and even respiratory depression significantly increases. The danger is even higher in older adults or those with underlying health conditions.
Examples of prescription and OTC sleeping aids you should never mix on your own with cannabis include:
If you have sleeping issues or have difficulty getting off of these medications, as many people do, your provider may be able to help you wean off of them using cannabis under their medical supervision.
Benzodiazepines are central nervous system depressants that slow down activity in your brain. This effect can help reduce anxiety, promote sleep, and relax muscles, making them useful for treating conditions like insomnia, panic disorders, and seizures.
However, mixing benzodiazepines with cannabis is potentially dangerous because both are central nervous system depressants. Their combined effects can amplify sedation, impair coordination, slow breathing, and increase the risk of accidents or overdose. The risk is even higher if you use benzodiazepines with high-THC cannabis, or if you are particularly sensitive to THC’s effects.
Benzodiazepines you shouldn’t use with cannabis on your own include:
Some epileptic patients, like those with Lennox-Gastaut Syndrome (LGS), may need to stay on some of these medications, like clobazam or clonazepam, and still take their prescription CBD. Specialist consultation is necessary before starting cannabis to account for blood labs, monitor for reactions, and adjust these doses over time.
Your provider can also create a safe tapering plan if you have benzodiazepine dependence and want to wean using cannabis, an approach still being researched.
If you’ve ever had the flu or allergies, you’ve likely used an antihistamine. They are widely available and easily accessible as OTC meds, such as Benadryl®. There are also stronger, prescription-only antihistamines for treating severe itching, hives, hay fever, and migraines.
Antihistamines are usually categorized as H1 or H2 blockers. H1 blockers are further divided into first-generation and second-generation allergy meds, while H2 antihistamines are used for acid reflux and stomach acid. First-generation H1 antihistamines can cross the blood-brain barrier and directly cause CNS-depressing side effects like drowsiness and brain fog – causing a potential interaction with cannabis – while second-gen and H2 antihistamines work differently and don’t have the same side effects or significant interaction potential.
Mixing first-generation, H1 OTC or prescription antihistamines with cannabis can cause excessive drowsiness, slowed breathing, and even respiratory depression. That’s because the sedative and nervous system depressant effects of both substances can stack and overwhelm your body, making it harder to stay alert and breathe properly. High doses may lead to dangerously slow breathing, unconsciousness, and an increased risk of accidents or overdose.
Examples of first-gen, H1 antihistamines that don’t interact well with cannabis include:
Doctors typically prescribe opioids to help patients treat acute or chronic pain. The pain may be from surgery, injury, cancer, or long-term conditions like arthritis or back problems.
Opioids typically treat pain by binding to opioid receptors in the brain, spinal cord, and other areas of the body. Doing so blocks pain signals, changing how the brain perceives pain. The medication may also make you feel euphoric and induce a sense of calm to distract you from pain.
Mixing such medications with cannabis is dangerous because their combined effects may intensify sedation, impair judgment, and dangerously slow breathing. Their stacked effects may also increase the risk of overdose, unconsciousness, and in severe cases, respiratory failure or death. As such, you shouldn’t mix weed with opioids without your doctor’s go-ahead and guidance.
Examples of opioids you shouldn’t mix with cannabis without medical supervision include:
READ: What Are the Risks of Combining Cannabis and Hydroxyzine?
Your prescribed antidepressants may be selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), atypicals (e.g., bupropion, mirtazapine, etc.), or monoamine oxidase inhibitors (MAOIs). While you may cautiously mix some of these classes of antidepressants with marijuana under your doctor’s guidance, TCAs and MAOIs pose the most risk with marijuana.
MAO inhibitors and weed may cause serious serotonin syndrome – a potentially life-threatening condition caused by too much serotonin in the brain. Symptoms include confusion, rapid heart rate, high blood pressure, muscle rigidity, unconsciousness, and even seizures. TCAs, on the other hand, may dangerously sedate, especially at higher doses.
However, don’t underestimate SSRIs, SNRIs, and atypical depressants. When used with cannabis, they may intensify common side effects like drowsiness, anxiety, dizziness, or mood swings. Cannabis may also interfere with how well these antidepressants work, but we don’t have enough long-term studies yet.
Popular versions of these antidepressants include:
Your doctor may prescribe an immunosuppressant to calm your immune system before or after an organ transplant, or more commonly to manage autoimmune diseases like lupus, rheumatoid arthritis, or Crohn’s disease.
Using cannabis alongside such medications can be problematic because THC and CBD interfere with CYP3A4, the liver enzyme that breaks down most immunosuppressants. This can make an immunosuppressant’s active ingredients accumulate in your blood, increasing the risk of toxicity and overdose. It can also compromise your treatment, raising the risk of infection, kidney damage, or organ rejection (although data are weak).
Organ donors may also be sadly excluded or rejected simply due to cannabis use out of precaution.
Examples of immunosuppressant drugs you should never mix with marijuana include:
Cannabis, specifically CBD, can help treat various types of seizures. In fact, FDA-approved CBD medications like Epidiolex® are available for treating severe seizure disorders in children and adolescents.
However, if you’re already using prescription anticonvulsants for your seizures, you shouldn’t use cannabis without your doctor’s go-ahead. That’s because CBD and other cannabinoids can interact with liver enzymes like CYP3A4 and CYP2C19, which process most anticonvulsants. The interaction may cause the medication to accumulate in your system, increasing the risk of side effects, toxicity, or reduced seizure control.
In studies involving the use of CBD and anti-epileptic drugs (AEDs) like valproate, several participants experienced adverse effects like rashes, fever, and liver enzyme elevation. Besides valproate (Depakene®), other anticonvulsants you shouldn’t mix with cannabis without medical supervision include:
Smoking or vaping cannabis, if you have asthma, is obviously ill-advised because it can worsen your respiratory health. Even if you don’t vape or smoke, cannabinoids can still pose a risk if you’re on asthma medication. Fortunately, emergency, life-saving asthma medicines like albuterol are not affected by cannabinoids.
Your body breaks down some asthma meds using CYP1A2, which is one of the enzymes that metabolize THC and CBD. As such, cannabinoids may interfere with how your body processes other asthma drugs, potentially causing dangerous drug level fluctuations. Possible adverse effects include increased heart rate, anxiety, dizziness, and trouble breathing, which is a big problem if you have asthma.
Asthma drugs not to mix with cannabis include:
Living with mental illness is hard, but with the right antipsychotic medication, a functional life becomes possible. However, cannabis can lower the effectiveness of antipsychotics and cause symptoms to resurge or even worsen.
Why? Many antipsychotics work by controlling dopamine activity. THC, which is a psychoactive compound, can interfere with this by increasing dopamine activity and counteracting the medication’s effects. This may worsen symptoms like paranoia, hallucinations, or anxiety.
Examples of antipsychotics you shouldn’t use with cannabis include:
While THC can make things worse for people with psychosis, CBD is emerging as a promising antipsychotic alternative or adjunct that offers multiple direct therapeutic effects while enhancing antipsychotic signalling. Attentive psychiatric care is needed for carefully combining CBD and conventional approaches.
Stimulants boost dopamine levels to help you focus and stay alert. Since cannabis, especially CBD, has an opposing effect, it can reduce the stimulant’s effect, making it harder to concentrate. This can trick you into using higher doses and increase the risk of dependence or side effects.
Also, since stimulants and THC can raise blood pressure and heart rate, combining the two can put you at risk of cardiovascular issues. For these reasons, don’t mix these prescription stimulants with weed:
On a case-by-case basis, your doctor may decide if it’s OK for you to mix THC, CBD, or both with your ADHD medicine, depending on your age, insight, and circumstances. Some adult patients can successfully use cannabis and ADHD meds under supervision for improving ADHD symptoms and alleviating the possible side effects of ADHD meds, like sleeping issues and appetite loss.
Several types of heart medications are available, and they help improve heart health through various means. For instance, some lower blood pressure, while others regulate heart rhythm to reduce the risk of heart attacks or strokes.
THC, especially at high doses, can have the opposite effect and increase heart rate and blood pressure in the short term until it is metabolized. This counteracts your heart meds, putting you at risk of complications like arrhythmias, chest pain, or even dangerous cardiac events.
If you are on any of these prescription heart drugs, talk to your doctor before using cannabis:
Keep in mind that our list of medications you should never mix with cannabis is NOT exhaustive! For your safety, don’t combine recreational or medical cannabis use with any other recreational substances like alcohol, or medication your body might process with CYP450 enzymes (like CYP3A4, CYP2C9, CYP2D6, CYP1A2) and UGT enzymes (like UGT1A9 or UGT2B7). This is the vast majority of medications, so it’s important to be cautious first and talk to your provider.
Your liver uses these enzymes to break down both cannabinoids and many prescription drugs. Combining both can lead to unpredictable drug levels, stronger side effects, increased toxicity, or reduced treatment effectiveness. However, it’s not a hard stop since your doctor should know how to evaluate these relative risks, order necessary labs, and make any dosage adjustments.
So, if you’re on any medication, including those not on our list, please consult your doctor before using cannabis in any form. They’ll let you know if it’s safe to use with your medication and how to use the combination with fewer risks.
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