For many people considering cannabinoid therapy, one of the most important questions is not simply: “Could cannabis help me?” It is: “Can I safely use it with the medications I already take?”

 

People seeking cannabinoid therapy may also be taking medications for epilepsy, pain, anxiety, depression, heart conditions, cancer, transplant care, sleep, or other chronic conditions. Older adults may take several prescriptions each day. And even a product marketed simply as “CBD” is biologically active.

 

Like many prescription medications, cannabinoids are processed by enzymes in the liver and other parts of the body. That means one substance can sometimes change how quickly another is metabolized, how much reaches the bloodstream, or how strongly its effects are felt.

 

While this does not mean cannabis cannot be used alongside prescription medications, it does mean cannabis belongs in the medication conversation.

 

The Short Answer

 

Yes, cannabis and cannabinoids can interact with some medications, but the clinical significance varies considerably.

 

Some interactions have been documented in human clinical trials while others are supported primarily by case reports or laboratory evidence. Some require additional monitoring or warrant a dose adjustment; and others may have little meaningful effect at the doses being used.

 

A 2024 systematic review of medical cannabis drug interactions evaluated 54 published studies and identified interactions involving 20 drug classes. The strongest body of evidence involved antiepileptic medications, with notable interactions also involving clobazam, warfarin and tacrolimus.

 

This is why a drug-interaction checker can be a useful starting point but shouldn’t be the end of the conversation.

 

The better question is not simply, “Do these two substances interact?” but “Is this interaction clinically meaningful for this person, at these doses, using this product?”

 

How Do Drug Interactions Happen?

 

There are two major ways to think about drug interactions: Pharmacokinetic interactions (changing how much drug is in the body) and Pharmacodynamic interactions (changing how the effects feel).

 

A pharmacokinetic interaction occurs when one substance changes the absorption, metabolism or elimination of another.

 

Many medications are metabolized through a family of liver enzymes called the cytochrome P450, or CYP450, system. Several cannabinoids use some of these same pathways.

 

The systematic review notes that THC is metabolized primarily through CYP2C9 and CYP3A4, while CBD is metabolized through CYP3A4 and CYP2C19. Both cannabinoids can also inhibit several CYP enzymes involved in processing other medications.

 

Think of these pathways a little like checkout lanes. If something slows one of those lanes down, another medication may remain in the bloodstream longer and reach a higher concentration than expected. In other situations, metabolism can be accelerated, potentially reducing drug exposure and making a treatment less effective.

 

A pharmacodynamic interaction is different. The concentration of a drug may not change substantially at all. Instead, two substances produce similar or opposing effects in the body.

 

For example, cannabis (particularly THC) may cause drowsiness or impairment. When combined with another medication that causes sedation, the combined effect may become more significant.

 

Of importance to note about these two interactions is that not every interaction will show up simply by checking a blood level.

 

Which Medications Deserve Particular Attention?

 

This is not a comprehensive list, and it should not be used to make medication changes without professional guidance. But current evidence gives us several useful examples.

 

Antiseizure Medications

 

This is currently one of the best-studied areas of cannabinoid drug interaction research.

 

In the 2024 systematic review, antiepileptic medications represented the drug class with the greatest amount of interaction evidence. One particularly well-established example is clobazam.

 

CBD inhibits CYP2C19, which helps metabolize clobazam’s active metabolite, N-desmethylclobazam. In studies reviewed by the authors, concentrations of that active metabolite increased substantially, with sedation among the observed adverse effects. Monitoring was recommended when CBD and clobazam were used together.

 

This interaction is also reflected in current FDA prescribing information for the purified CBD medication Epidiolex: coadministration increased exposure to N-desmethylclobazam by approximately threefold.

 

Valproate presents a different example.

 

Studies have generally not found a clinically meaningful increase in valproate concentration when it is taken with CBD. However, elevations in liver enzymes have occurred more frequently when the two are used together. The review therefore emphasizes routine liver-function monitoring. This is a perfect illustration of why cannabinoid interactions cannot be reduced to one question about drug levels.

 

Blood Thinners

 

Warfarin deserves particular caution because relatively small changes in its activity can affect the risk of bleeding or clotting.

 

CBD can inhibit CYP2C9 and CYP3A4, enzymes involved in warfarin metabolism. Case reports have documented increasing INR values as CBD doses increased, followed by improvement after the warfarin dose was adjusted.

 

In one case summarized in the review, INR increased from 2.22 to 6.86 following CBD titration; the patient’s warfarin dose was subsequently reduced.

 

A separate systematic review of cannabinoids and anticoagulants similarly found that the evidence is still low quality but consistently points to warfarin as an interaction clinicians should recognize.

 

For someone taking warfarin, beginning cannabis or CBD (or substantially changing the dose or product) is therefore something the prescribing clinician should know about.

 

Transplant and Immunosuppressive Medications

 

Medications such as tacrolimus, everolimus and sirolimus are particularly important because maintaining drug concentrations within an appropriate range is critical.

 

The evidence with tacrolimus is limited and somewhat inconsistent, but clinically important increases have been reported. One case included in the review found an approximately threefold rise in dose-normalized tacrolimus concentration along with evidence of kidney toxicity.

 

Everolimus concentrations have also increased when administered with CBD; current FDA information reports an approximately 2.5-fold increase in everolimus exposure in a drug-interaction study.

 

For transplant recipients or others using medications with narrow therapeutic ranges, cannabinoid use should be discussed directly with the clinical team rather than managed independently.

 

Antidepressants and Other Sedating Medications

 

The evidence here is less developed, but there are reasons for caution.

 

Citalopram and escitalopram are metabolized in part through CYP2C19 and CYP3A4 (pathways that CBD can inhibit). One small study involving six participants found increased citalopram concentrations with CBD. The authors also noted another concern: cannabis and some antidepressants can independently cause sedation or cognitive effects, making additive effects possible.

 

Similar caution applies when cannabis is combined with other medications that can cause drowsiness or impairment, including certain:

 

• benzodiazepines;
• sleep medications;
• opioids;
• gabapentinoids; and
• other central nervous system depressants.

 

This does not mean those combinations are automatically prohibited, rather it means sedation itself is an interaction worth monitoring.

 

What About Opioids?

 

The 2024 review found clinical studies in which cannabis administered with morphine or oxycodone enhanced analgesic effects without significant changes in opioid pharmacokinetics, although participants also reported subjective psychoactive effects. The authors emphasize that the evidence remains limited and that mechanisms are not firmly established.

 

A case involving methadone and CBD, however, documented increased methadone concentrations along with fatigue and somnolence that improved following CBD withdrawal.

 

So “opioids” cannot be treated as one interaction. The particular medication, cannabinoid, dose and patient all matter.

 

The Dose, Product and Route Matter Too

 

This is one of the most important, and most frequently overlooked, limitations of cannabinoid drug-interaction research.

 

A 10 mg full-spectrum CBD capsule is not pharmacologically equivalent to several hundred milligrams per day of pharmaceutical isolate CBD. Neither is an inhaled high-THC product equivalent to an oral CBD oil.

 

The authors of the systematic review specifically caution that interaction outcomes may differ according to the type and amount of cannabinoid absorbed, formulation used and route of administration. Oral cannabinoids undergo more extensive first-pass metabolism through the liver than inhaled forms, for example.

 

That means a study demonstrating an interaction at a particular dose and formulation does not automatically tell us the magnitude of interaction from every commercially available product. It also means patients should be as specific as possible when talking with healthcare professionals.

 

Instead of saying: “I use CBD.” Try: “I take 25 mg of CBD by mouth twice a day, and the product contains approximately 1 mg of THC per serving.”

 

Product name, cannabinoid content, amount, frequency, route of administration and timing can all help make the conversation more clinically useful.

 

An Interaction Does Not Always Mean “Stop”

 

An important takeaway is that a potential drug interaction does not automatically mean that two therapies can never be used together.

 

In many of the studies included in the review, clinicians managed interactions through closer laboratory monitoring, watching for adverse effects, adjusting doses, or discontinuing one treatment when necessary. That is already how medicine handles many other drug interactions.

 

A clinician may:

 

• check medication blood levels more frequently;
• monitor liver or kidney function;
• monitor INR;
• watch for excess sedation or other symptoms;
• adjust the dose of a prescription medication;
• adjust cannabinoid dose or timing; or
• decide that a particular combination carries more risk than benefit.

 

What patients should not do is independently stop or alter an important prescription medication because an online interaction checker produces a warning, rather allow the warning to lead your conversation with your physician.

 

A Special Situation: Cannabis and Surgery

 

Surgery is one time when disclosure of cannabis use is particularly important. Anesthesiologists need to know about all medications, supplements and cannabinoid products because cannabis use may affect anesthesia requirements, cardiovascular and respiratory risk, postoperative pain treatment, nausea and vomiting, withdrawal, and interactions with medications given before, during or after a procedure.

 

Current recommendations support screening patients before surgery for cannabinoid use and asking about the:

 

• type of product;
• THC and CBD content when known;
• route of administration;
• amount and frequency;
• reason for use; and
• time of most recent use.

 

Patients should not arrive at surgery assuming that CBD “doesn’t count” because it is non-intoxicating. CBD is still pharmacologically active and is metabolized through pathways shared by many medications.

 

Likewise, a person using cannabinoid therapy for epilepsy, severe pain or another medical condition should not abruptly discontinue treatment solely because surgery is approaching. The surgical and anesthesia teams can help determine an appropriate plan.

 

Current ASRA guidance advises postponing elective surgery when a patient has altered mental status from acute cannabis intoxication and delaying elective surgery for at least two hours after cannabis smoking because of acute cardiovascular effects. Beyond that, timing recommendations depend on factors including the product, route, frequency of use and patient’s medical circumstances.

 

Read more: What to Know About Cannabis Use and Surgery.

 

What We Still Don’t Know

 

Drug-interaction research is expanding, but significant gaps remain. The 2024 review itself notes that much of the available evidence consists of case reports, that dosing and formulations are inconsistent, and that the duration of many studies is short.

 

A 2025 scoping review examining CBD interactions found 271 reported interactions across the literature, most involving pharmacokinetic mechanisms. Yet only 5.15% of included studies evaluated the clinical relevance of those interactions.

 

In other words: We know enough to take drug interactions seriously. We do not know enough to treat every theoretical interaction as a clinical emergency.

 

We still need better research addressing:

 

• commonly used real-world cannabinoid doses;
• THC as well as CBD;
• minor cannabinoids such as CBG, CBDA and CBN;
• different routes of administration;
• long-term use;
• older adults and polypharmacy;
• commercially available formulations; and
• which laboratory interactions actually translate into meaningful patient outcomes.

 

These gaps are not reasons to exclude cannabinoid therapy from healthcare, they are reasons to bring it more fully into healthcare.

 

How to Have a Better Conversation With Your Healthcare Team

 

If you use cannabis or cannabinoid products alongside prescription medications, consider bringing your healthcare professional or pharmacist the same information you would provide about any other treatment:

 

What are you taking?
Include CBD, THC and other cannabinoids when known.

 

How much are you using?
Provide milligrams per serving when available.

 

How are you taking it?
Oral, sublingual, inhaled and topical products may behave differently.

 

How often do you use it?

 

What are you using it for?

 

What other medications, supplements or over-the-counter products do you take?

 

Have you recently increased, decreased or changed your cannabinoid product?

 

Have you noticed anything different since combining them?

 

A productive healthcare conversation does not require a patient to prove that cannabinoid therapy is good or bad. It requires enough information to make an informed decision together.

 

Cannabis Belongs on the Medication List

 

For too long, many patients have felt that cannabis use was something they should keep separate from the rest of their healthcare. Drug-interaction research demonstrates exactly why that separation does not work.

 

If cannabinoids can influence the metabolism or effects of prescription medications, then clinicians need to know when their patients use them. And patients need to feel safe enough to tell them.

 

The goal is not to frighten people away from cannabinoid therapy. It is also not to assume that because something is plant-derived or available without a prescription, interactions cannot occur. The goal is informed, individualized and responsible care.

 

At Realm of Caring, our Care Team provides free education to individuals and families navigating cannabinoid therapy, including helping clients understand the questions they may want to bring to their physician or pharmacist.

 

Have questions about your cannabinoid regimen? Connect with our Care Team.

 

Already using cannabis or cannabinoids? Participate in research and help build the evidence clinicians need.

 

The more cannabinoid therapy becomes part of healthcare, the less patients should have to navigate these questions alone.

 

This information is intended for educational purposes and is not a substitute for individualized medical advice. Do not begin, stop or change a prescription medication or cannabinoid regimen based solely on this article. Discuss potential interactions with an appropriate healthcare professional or pharmacist.