“Generally,” Bednarczyk says, “CBD is thought to inhibit metabolic pathways, and THC is thought to induce metabolic pathways. THC can make your blood levels of other drugs fall, and CBD can make your blood levels rise.”
Warfarin, CBD a dangerous combo
One well-known example is warfarin, “a very, very potent blood thinner,” Bednarczyk says.
A case study published a couple of years ago says one warfarin patient “had the effects of this drug go way up into the danger zone shortly after starting CBD.” “That one, you don’t mess with. The effects of having too high a level even transiently for a few days can be lethal,” he warns.
“That’s the king of the hill for risk, because it’s all over the map in terms of patient-to-patient variability,” Bednarczyk says of warfarin and pot. “One patient can need a bucket of this stuff to have the same effect as another patient who’s on the lowest dose manufactured.”
The opposite occurs when you mix pot with tamoxifen, a hormone therapy drug used to treat breast cancer by blocking the effects of estrogen, Lazarus adds.
For tamoxifen to work, he notes, it must be broken down by the body into another chemical called endoxifen, which is 100 times more active than tamoxifen.
If pot interferes with the processing of tamoxifen, it could cause the breast cancer patient to receive little to no benefit from the drug, Lazarus explains.
Lazarus says he’s also concerned about the interaction pot might have with over-the-counter pain medications.
Ibuprofen is toxic to your liver and your kidney anyway, but if you start taking marijuana on top of that, then you’re going to see some significant effects,” Lazarus says. “It would probably cause toxicity because you’re slowing down its metabolism, so that means you’re not excreting the stuff and you have more of it sitting in your body.”
However, all these concerns are based on lab studies. What’s needed now are clinical trials to establish the true effects of pot on other drugs, Lazarus notes.
“We have to do some clinical studies to show in people that if you’re taking a specific drug and then you also smoke a marijuana cigarette that morning, you see higher or lower levels of that drug in your body,” Lazarus said.
In the meantime, people should discuss their use of pot products with their doctor and their pharmacist to make sure they aren’t putting their health at risk, Lazarus and Bednarczyk suggest.
“This should not be a roll-your-own process,” Bednarczyk concludes.