By Dr. Mary Frances Koester
Many patients suffering from a variety of medical conditions do not get adequate relief using traditional medications. Medical marijuana is proven as a safe, natural, and effective alternative or adjunct to many medications. But as patients begin to consider medical marijuana as an alternative, a common concern is whether marijuana will interfere with their prescription medications or herbal supplements. Unfortunately, while the use of marijuana for medicinal purposes has skyrocketed, the research about marijuana is lagging far behind. This is because marijuana, despite its medicinal legality in many states, is federally illegal and considered a Schedule I drug which places a nearly impenetrable barrier on research. The tide is turning and currently many large university medical systems are studying marijuana. Based on the research we have, we do know that there is definitely potential for marijuana to interact with certain medications.
A Little Chemistry
The majority of prescribed medications are metabolized, or broken down, by the liver by cytochrome p450(CYP) enzymes. These enzymes are the reason for many drug-drug interactions. Some medications make the CYP enzymes more active while others inhibit them. This means that a drug which activates the CYP enzymes causes the medication to be metabolized (broken down) faster. A drug which inhibits the CYP enzymes slows down the metabolism (break down) of the medication resulting in an accumulation of the drug in the body and, with that, possible side effects and even drug toxicity.
Why Medical Marijuana May Interfere with Your Medication
Marijuana can theoretically either increase or decrease the concentration of certain medications. As well, certain medications can increase or decrease concentrations of marijuana. This is because THC and CBD are metabolized by CYP2C9 and CYP3A4. Thus, if another medication inhibited this enzyme, it would, in theory, be expected to inhibit the elimination of THC and thereby increase the concentration of THC. One study did show that ketoconazole, an inhibitor of CYP3A4, increased concentrations of THC1.2-1.8 fold. In general, the CYP3A4 inhibitors slightly increase THC levels while the drugs that are CYP3A4 inducers slightly decrease THC and CBD levels.
Because THC is a CYP1A2 inducer, theoretically, it can decrease the amount of certain drugs that are broken down by that enzyme by speeding up the breakdown. This means they may be less effective. Some drugs that are metabolized by CYP1A2, thus may be decreased by marijuana use are:
CBD is a potent inhibitor of CYP3A4 and CYP2D6. Because CYP3A4 metabolizes about a quarter of all drugs, CBD may increase serum concentrations medications such as:
- Calcium channel blockers
- Some statins (atorvastatin and simvastatin)
The CYP2D6 enzyme metabolizes some pain medications and many antidepressants, so CBD may also increase serum concentrations of
- Tricyclic antidepressants,
- Beta blockers
Is There Evidence of Marijuana Interfering with Medications?
So yes, in theory, marijuana can decrease the efficacy of your medication by increasing its breakdown in the body or it can increase the concentration of your medication by slowing down the breakdown. But is there evidence that it actually has a clinically significant effect? There is a paucity of literature as stated before. There are some case studies of patients taking the blood thinner Warfarin having increased INR levels resulting in the need to reduce the amount of warfarin they were taking. As well, one study in children using CBD for treatment of severe seizure disorder were noted to have elevated levels of clobazam. For now, the existing data is insufficient to accurately characterize drug interactions of marijuana or its constituents with other medications. I advise all medical marijuana patients to make sure that their prescribing physicians know that they are taking medical marijuana and aware of potential interactions. I also warn all of my patients who are taking blood thinners to monitor their INR when applicable and to watch for increased bruising or bleeding.
About the Author
Mary Frances Koester, MD graduated from Franklin and Marshall College and received her MD/MBA from Temple University School of Medical and Fox School of Business. She went on to complete her residency in Emergency Medicine. After seeing so many patients suffering from opioid and benzodiazepine addictions as well many suffering from untreated chronic pain or anxiety, she began her education in marijuana medicine. She believes in the benefits of medical marijuana and advocates its use as a safe and effective alternative to traditional medications. Her mission is to create a true medical practice that strives to provide ongoing and meaningful care for her patients.