CBD and Drug Interactions

Researchers generally agree that for the majority of people, CBD oil is a safe and beneficial therapy, unlikely to cause any side effects. But, there are three specific groups of people they caution against taking CBD oil: 

Considering about half of Americans take at least one prescription drug, that could put CBD out of reach for a large number of people. If you’re one of those people, how much are you risking by mixing your medication with CBD? Are certain medications higher risk than others?

While researchers are finding many benefits to CBD oil, from arthritis to stress relief, the field of research is still new. Researchers don’t yet know how CBD might interact with the full universe of medications available today. They have discovered, however, that CBD may affect the liver’s ability to metabolize certain drugs, much like grapefruit. 

Below we review the existing research about CBD’s potential drug interactions, so you can be more informed about the wellness choices you make.

Note: This article does not constitute medical advice. If you are taking other medication, it’s extremely important to consult with your doctor first, before taking CBD oil. They know your health history, they’re aware of your current drug regimen, and they can best advise you as to whether you should expect side effects when taking CBD. Moreover, they may be able to change out some of your other medication to accommodate CBD oil, or advise you on other lifestyle changes you can make to further relieve your symptoms.

Can CBD Oil Interact with Medications?

If you want a simple answer to the question “Can CBD oil interact with medications?”, here it is: If the drug has a grapefruit warning, or if your doctor tells you to avoid eating grapefruit while taking the drug, you should likewise avoid taking CBD oil.

The research is still developing on CBD and drug interactions, but there’s one thing we do know. CBD has a similar effect to grapefruit on your body’s ability to metabolize other drugs. (Grapefruit and CBD shouldn’t be singled out, however. Herbal remedies that have a similar effect include St. John’s Wort and goldenseal.)

Comparing CBD to grapefruit is a simple explanation. Specifically, CBD inhibits the cytochrome P450 enzyme system. The cytochrome P450 enzyme system contains over 50 enzymes, six of which metabolize about 90% of the drugs we consume. Whenever you take a drug, these enzymes work to break down the drug’s chemicals into substances your body can use. When you take CBD, it temporarily deactivates these cytochrome P450 enzymes. As a result, your body has a tougher time breaking down the drugs you’ve ingested. This effect is amplified in large doses of CBD. 

Because CBD inhibits these enzymes, it can cause a higher concentration of the drug to stay in your system longer than it should. As a result, you may experience negative side effects. 

The risk increases when you consider how doctors prescribe medication. In part, doctors recommend dosage amounts and frequencies based on the standard amount of time it takes the cytochrome P450 enzyme system to metabolize the drug. If you don’t share with them your full drug history (including any CBD oil you’re taking), the dose they recommend may be higher or lower than it should be. 

What Drugs Should Not Be Taken with CBD?

Within the cytochrome P450 system, CBD inhibits two enzymes specifically: CYP3A4 and CYP2D6. CYP3A4 metabolizes around 25% of all drugs, including calcium channel blockers, benzodiazepines, antihistamines, antiretrovirals, macrolides, cyclosporine, sildenafil, and statins like atorvastatin and simvastatin. CYP2D6, on the other hand, primarily metabolizes antidepressants, including SSRIs, tricyclic antidepressants, antipsychotics, beta blockers, and opioids.

Below is a list of drugs which are metabolized by the cytochrome P450 system. While not an exhaustive list, these drugs may be impacted by CBD:

  • Antidepressants
  • Benzodiazepines
  • Calcium channel blockers
  • Blood thinners
  • Antibiotics
  • Steroids
  • Beta blockers
  • Pain relievers
  • Antiepileptics
  • Antihistamines
  • NSAIDs
  • HIV antivirals
  • Antipsychotics
  • Statins

You can view a full list of CBD’s drug interactions on sites like MedlinePlus and American Academy of Family Physicians. Even if the medication you’re taking is not on one of these lists, it’s still safest to consult your doctor before taking CBD.

Does CBD Affect Blood Pressure Medication?

In healthy individuals, CBD has been shown to reduce anxiety. It can also reduce the blood pressure response to stress:

cbd can lower blood pressure and anxiety

Beta blockers reduce blood pressure and slow the heart rate. Beta blockers are often prescribed to treat individuals with anxiety, high blood pressure, or other heart conditions, so you might wonder if CBD may enhance the effectiveness of these medications. However, because CBD affects the metabolization of these drugs, your blood pressure may drop too much if they’re taken together. Your heart rate may slow further, as well, and you might experience other side effects of the medication—such as feeling weak or dizzy. 

Does CBD Oil Thin the Blood?

Studies show that CBD can act as a mild coagulant, thinning the blood. For those taking Warfarin (coumadin) or another blood thinner, this may prolong the effect of your dose and temporarily increase the thinning of your blood, as CBD increases the level of the drug in your blood. 

In one case study, a patient taking Warfarin was given a daily regimen of CBD, which increased in dosage every two weeks. His goal INR was 2 to 3. INR (or International Normalized Ratio) is a measurement of how quickly your blood clots. An INR that is too low will prevent blood clots, while an INR that is too high can increase the risk of bleeding. People who take blood thinners to treat blood clots are often given a goal INR of 2 to 3, like this patient (for comparison, the INR for healthy people is around 1). 

As the study progressed, the higher doses of CBD oil increased the patient’s INR, so the physician had to keep lowering his Warfarin dose in order to keep his INR within the therapeutic range:

cbd can increase inr for patients on warfarin

Does CBD Oil Interact with Antidepressants?

Several studies have indicated CBD provides anti-depressant and anti-anxiety effects for those suffering from social anxiety disorder or PTSD. What if you combine CBD oil with an antidepressant medication? 

To find out, researchers created a clinical model using mice, who were given both antidepressants and CBD oil. The study found that adding the CBD oil produced a “synergistic” effect, suggesting that CBD may enhance the antidepressant effect provided bySSRI medication. However, SSRI antidepressants like fluoxetine (Prozac) and paroxetine (Paxil) do interact with the cytochrome P450 enzyme system, so it’s still best to speak to your doctor before mixing these.

Does CBD Oil Interfere with Birth Control?

There is little to no research on CBD’s effect on birth control. Anecdotally, many people take CBD oil while on birth control and report no side effects. 

However, studies do suggest cannabis may interfere with the effectiveness of birth control. For example, a 1991 study observed that cannabinoid exposure (particularly to THC) inhibited hormone release

Even though this study focused primarily on THC, it does reinforce the fact that it’s important to speak with your doctor before combining CBD with your birth control. Birth control medications may rely on the cytochrome P450 enzyme system, so high doses of CBD oil may reduce their effectiveness as a contraceptive.

Can CBD Oil Interfere with Antiepileptic Drugs?

The benefits of CBD for epilepsy have been demonstrated, perhaps more so than for any other condition. The evidence is so strong, in fact, that the only FDA-approved drug containing CBD is prescribed for severe forms of pediatric epilepsy.

But despite the effectiveness of CBD for managing the symptoms of epilepsy, researchers have documented its potential to increase the serum levels of certain antiepileptic drugs (including clobazam, rufinamide, topiramate, zonisamide, and eslicarbazepine). CBD may also impair liver function in epileptic patients. These risks increased with higher amounts of CBD. If you are considering using CBD oil to manage epilepsy symptoms, please speak with your doctor first.

CBD and Drug Interactions: Other Factors to Consider

To date, much of the research suggests that the biggest risk for those taking other medications occurs with high doses of CBD. However, you should still consult your doctor before taking CBD, regardless of the dosage amount.

There are other factors that could impact CBD’s interaction with your existing medication. These include when you take the CBD oil, and how you take it. For example, you and your doctor may be able to work out a dosing regimen where you can take CBD at a different time of day than your other medication, allowing one to be metabolized sufficiently enough to lower the risk of any potential impact.

The potency of a CBD oil largely depends on the method of administration. In other words, how you choose to ingest CBD can impact its bioavailability (or how much of the CBD ultimately gets absorbed into your bloodstream). For example, a 20mg dose of CBD administered through a vaporizer is likely to be significantly more potent than one administered topically

Generally, CBD administered through inhalation tends to have the highest bioavailability, followed by (in descending order) sublingual administration, oral ingestion and topical application. This is also an area where you doctor can help. If they deem it safe for you to use CBD, they may suggest a different dose of CBD depending on your preferred method of administration. 

The Final Word: CBD and Drug Interactions

To wrap up, doctors don’t know the full scope of CBD’s ability to interfere with medications. Based on the current research, it seems to have a similar effect to grapefruit. If you are taking any medication that has a grapefruit warning, you should avoid taking CBD oil.

However, CBD’s inhibition of the cytochrome P450 enzyme system means it has the potential to interfere with 90% of the drugs out there. So, even if your medication doesn’t have a grapefruit warning, you should always consult a doctor before taking CBD oil, to avoid it interfering with the efficacy—or safety—of the other prescription or over-the-counter drugs you’re taking.

There’s one more thing to keep in mind when considering the safety of mixing CBD with other medications. As a new industry, CBD isn’t regulated by the FDA. That means manufacturers with both good and bad intentions can peddle their CBD oils to consumers. And because things are unregulated, you can never be sure of whether the additional ingredients present in the CBD product could likewise interfere with your medication. Some brands may not even provide a full, honest list of ingredients on the bottle. Furthermore, many full-spectrum CBD oils contain other cannabinoids besides CBD, including THC—albeit in trace amounts. These could produce their own adverse effects when mixed with your medications.

Regardless of whether you’re taking other medications or not, you can make a safer CBD purchase by buying from well-known, reputable brands who partner with unbiased third-party labs to test their products for safety and purity; only use genuine CBD oil (and not synthetic versions); and are transparent about sharing their hemp sourcing and production methods with consumers. Learn more about how to safely buy CBD oil in our Guide to CBD Oils.

Additional Resources