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Medical Marijuana and Interactions With Other Medications: What Patients Need to Know

With the rise of cannabis use for different health conditions, patients need to be informed about the potential risks and benefits of combining it with prescription medications.

The use of cannabis can often replace prescription medications that are more addictive or dangerous, despite some interactions that can be harmful.

NOTE: The information here is not medical advice. This article is for educational purposes. Always talk to a healthcare professional about medication interactions before starting cannabis.

What are Medication Interactions?

Also called a contraindication, a medication interaction happens when someone takes two or more medicines that interact well together. The negative interactions can be serious or even life-threatening, so it’s very important to talk to your doctor before using prescription medications and medical marijuana.

The Role of Liver Enzymes in Drug Interactions

Liver enzymes are the unsung heroes of our bodies, tirelessly working to metabolize and eliminate different substances, including medical marijuana and other drugs.

One of the key enzymes involved in this process is CYP3A4, which is responsible for metabolizing many medications, including cannabis.

But this hardworking enzyme can also be the root cause of drug interactions, affected by different factors, such as:

  • The presence of other medications or substances in the body
  • Genetic variations in enzyme activity
  • Age and overall health of the individual
  • Liver disease or dysfunction

Known Interactions and the “Grapefruit Effect”

The “grapefruit effect” refers to the ability of both CBDs to inhibit the CYP3A4 enzyme, which can lead to drug interactions with cannabis, similar to how grapefruit juice works.

Inhibition of this enzyme by CBD can disrupt the breakdown and elimination of other drugs, causing elevated levels of these drugs in the bloodstream. This could potentially heighten the risk of side effects or alter the effectiveness of the medications.

Interactions Between THC/CBD and Other Drugs

Research suggests that delta 9 tetrahydrocannabinol THC and CBD in cannabis may interact with other drugs, such as opioids and blood thinners.

Cannabis and Opioids: A Delicate Balance

Cannabis has been found to activate cannabinoid receptors CB1 and CB2, interfering with the physiological actions of pain receptors and resulting in reduced pain perception.

This has led to its use in combination with opioids to achieve a synergistic effect, potentially reducing opioid use, improving quality of life, and augmenting the analgesic effects of opioids.

But this delicate balance comes with risks, as the simultaneous use of cannabis and opioids carries a heightened risk due to the combined depressant effects they have on the central nervous system.

Tapering opioid use can be beneficial for avoiding drug interactions with cannabis by:

  • Decreasing the dosage of opioids in the body
  • Lessening the possibility of interactions between opioids and cannabis
  • Reducing the risk of adverse effects.

Again, consult your doctor before mixing medical cannabis with opioids.

Anticoagulant Alert: Medical Marijuana Use and Blood Thinners

THC and CBD interactions with the CYP2C9 enzyme can increase Warfarin levels, potentially leading to excessive bleeding. This alarming interaction underscores the importance of avoiding cannabis use if taking blood thinners.

Avoid using cannabis if you’re on a blood thinner like Warfarin, just to be safe.


Valproate, also known by brand names like Depakote, Epilim, and Convulex, is a versatile anticonvulsant used to treat seizures, stabilize manic episodes in bipolar disorder, and even help with migraine headaches.

Studies suggest that it’s not a good idea to take cannabis or CBD if you’re on anticonvulsants like Valproate.


If you have asthma, emphysema, or chronic bronchitis and are treated with Theophylline, be careful about potential drug interactions with medical cannabis.

Smoking medical marijuana can cause your liver to process Theophylline faster, reducing the drug’s effectiveness. Edibles might have fewer risks with this medication.

On the other hand, compounds in cannabis like THC and terpenes like pinene can help open up the airways, which can be helpful for people with lung conditions.

Special Considerations for Specific Patient Groups

Certain patient groups taking psychiatric medications and antibiotics should be careful when using cannabis, as it can affect the efficacy of their medications and potentially cause side effects.

Psychiatric Medications and Medical Cannabis

Cannabis can interact with psychiatric medications, particularly tricyclic antidepressants (TCAs) such as Amitriptyline, Imipramine, and Dothiepin.

This interaction can cause symptoms such as a rapid heartbeat or an increase in blood pressure, which can be concerning for patients who rely on these medications to manage their mental health.

If you’re using medical cannabis and TCAs and feel a rapid heartbeat (tachycardia) or high blood pressure (known as hypertension if it lasts), it might be a reaction to the cannabis. Stop using cannabis and talk to your doctor.

Mixing cannabis with TCAs could lead to confusion, restlessness, hallucinations, and mood swings. If you think cannabis is affecting how your antidepressants work, don’t stop taking your psychiatric medications without a doctor’s help. It’s usually safer to stop using cannabis.

Antibiotics and Immunomodulation

While there is currently no definitive evidence that cannabis interferes with antibiotics, some studies suggest that it may even make them more effective in some instances.

You still need to consult your doctor if cannabis will be used while on a regimen of antibiotics, as it may interact with certain antibiotics and affect their efficacy.


Some sedatives might not mix well with cannabis, while others can be adjusted to work with it.

Clobazam for example, is used to reduce seizures in Lennox-Gastaut Syndrome (LGS), a type of childhood epilepsy. CBD can enhance the effects of Clobazam, but there’s some debate about this.

Some studies suggest it’s not a good idea to use them together, while other experts use this interaction to their advantage.

In cases where CBD and Clobazam are used together, doses are adjusted to minimize their sedative side effects.


CBD naturally suppresses the immune system, so if you’re taking other immunosuppressant drugs, like steroids such as Prednisone or anti-rejection pills for organ transplants, it’s important to talk to your doctor about any possible good or bad interactions.

There’s a chance CBD could help patients with kidney transplants, but more research is required for this.

What About Over-the-Counter Medications?

Using over-the-counter (OTC) medicines with acetaminophen along with cannabis might, though rarely, raise the risk of liver damage. Non-steroidal anti-inflammatory drugs (NSAIDs) can also have bad reactions to cannabis, potentially causing nervous system issues such as meningitis and the risk of bleeding.

But medical cannabis can often help reduce the need for OTC pain medications, and fortunately, there’s usually little interaction with most non-opioid OTC pain relievers.

Guidelines for Safe Use of Medical Cannabis and Other Medications

Consulting with a Healthcare Provider

Doctors and pharmacists play an important role in helping patients navigate drug interactions with cannabis.

They can provide valuable information about:

  • Potential interactions between various substances and medications
  • Adjusting dosages
  • Monitoring symptoms
  • Ensuring the safety and effectiveness of cannabis use

Adjusting Dosages and Monitoring

When including medical cannabis in a treatment plan that includes other medications, several key factors must be considered to adjust dosages safely and effectively.

These include:

  • Previous Experience with Cannabis: Understanding a patient’s history with cannabis can provide insights into potential tolerance levels and reactions.
  • Body Weight: Dosage requirements can vary significantly based on body weight, influencing how the body metabolizes both cannabis and other medications.
  • User Experience: The individual’s level of familiarity with cannabis can impact their response to the treatment.
  • Patient-Specific Considerations: Critical factors such as age and liver or kidney function play a significant role in how both cannabis and medications are processed by the body.

Talk to Your Doctor About Mixing Medical Marijuana with Other Medications

It is a good idea to consult your doctor first when considering using medical marijuana with other medications. It’s best to avoid mixing cannabis with medications like opioids, sedatives, and blood thinners, as well as tricyclic antidepressants.

Remember, different cannabinoids can affect the endocannabinoid system and other receptors in different ways. Keep in mind that not all cannabis has the same effect.

You might even find cannabis useful in reducing or replacing certain prescription drugs, particularly those that are more dangerous or addictive.

To safely enjoy the benefits of medical marijuana, consider getting your own medical marijuana card at TeleLeaf‘s HIPAA-compliant platform.

We are patients and caregivers—from the founders to our phone operators—so we know how important quick access to effective, safe medicine is for patients.


Drug interactions with cannabinoids – NIH

Grapefruit and medication: A cautionary note – Harvard Health

Medicinal Cannabis—Potential Drug Interactions – NIH

An interaction between warfarin and cannabidiol, a case report – NIH

Compound derived from marijuana interacts with antiepileptic drugs – Science Daily

Cautions – Antidepressants – NHS

Cannabinoids-Promising Antimicrobial Drugs or Intoxicants with Benefits? – NIH

CBD & Organ Transplant – Project CBD

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