Penn State College of Medicine researchers have found products containing cannabinoids may have impacts on the effects of some conventional prescription drugs.

The researchers have put together a list of 57 medications that may not function as intended when used with cannabis products including medical cannabinoids, CBD oil and medical or recreational marijuana. This could involve prescription drugs not being as effective, or their effects boosted. All the prescription drugs listed have a narrow therapeutic index – meaning the doses are usually prescribed at levels high enough to be effective, but not at a level that could cause harm.

There are some widely used medications on the list including warfarin, which is an anti-coagulant that prevents blood clots from forming.  Warfarin is commonly used to prevent stroke in patients with atrial fibrillation, valvular heart disease or artificial heart valves. Other classes of drugs include, but are not limited to, antibiotics, anti-convulsants and pain medications.

The researchers, Professor Kent Vrana and pharmacist Paul Kocis, have also published a list of 139 medications that could have a potential drug-drug interaction with a cannabinoid.

This is important research that demonstrates why it’s important for doctors to brush up on cannabis and for patients to be honest with their doctors about their cannabis use, whether its medicinal or recreational.

“As ∆9-THC and CBD over-the-counter (OTC) products and prescription medications are becoming increasingly available from a pharmacy, dispensary, Internet, local retail store, or by illicit means, there is an increased likelihood of an unintended drug-drug interaction when coadministered with another herbal, OTC, or prescription medication,” state the pair.

Their study has been based on prescribing information for four prescription cannabinoid medications – Dronabinol (Marinol and Syndros) CBD (Epidiolex) and Nabiximols (Sativex) – and comparing that to prescribing information for common medications. They stress the lists of potential drug-drug interactions are not intended to be a substitute for medical decision making, as the various and wide-ranging characteristics of each patient also need to be taken into account

The researchers’ work has been published in the journal Medical Cannabis and Cannabinoids. Additional commentary has been published on the Penn State website.