Cannabis interacts with certain medications like the blood thinner warfarin and many anti-seizure medications. The interaction comes from multiple drugs competing for the machinery in our bodies that metabolize and clear out substances.
Cannabis has been thrust into the limelight in recent years, with nearly half a million Pennsylvanians involved in the state’s Medical Marijuana Program, and almost two-thirds of Americans who support legalizing the drug federally, by one recent survey.
But cannabis is still a drug — and therefore can interact with other medications you may be taking.
“There are great things about cannabis and its potential, but there should be a cautionary tale in there as well,” said Kent Vrana, chair of the department of pharmacology and director of the Medical Marijuana Academic Clinical Research Center at Penn State University.
For one, cannabis interacts with certain medications like the blood thinner warfarin and many anti-seizure medications. The interaction comes from multiple drugs competing for the machinery in our bodies that metabolize and clear out substances.
“Our livers are built to filter toxins from our blood,” explained Vrana, adding that 57 genes in our DNA code are for enzymes responsible for doing so —but six of them alone are responsible for breaking down 90% of the drugs we ingest.
One of those main players is the cytochrome P450 pathway, a specific pathway that clears prescription drugs from our bodies.
That also means if you take multiple prescriptions, they’ll often compete to be broken down first by the liver. Even natural substances we ingest, such as grapefruit juice and supplements like St. John’s wort, are broken down via the CYP450 pathway.
This can be dangerous particularly for people who take warfarin and use cannabis. When someone uses cannabis, its chemicals interfere with the breakdown of warfarin.
“They’re tying up the enzymes so they can’t work on warfarin,” he explained. This can lead to a warfarin spike in the bloodstream, boosting the person’s INR (international normalized ratio, which is a measure of how long it takes for the blood to clot), further thinning the blood and increasing the risk of bleeding.
This trend is exacerbated with higher doses and concentrations of cannabis: one might see a larger interaction, say, if they smoked 100% THC isolate from a weed pen or dabbing rig, versus taking a couple puffs of cannabis flower.
Other notable medications that interact with cannabis include the tricyclic antidepressant amitriptyline, the immunosuppressant tacrolimus, anti-seizure medications carbamazepine, valproic acid and phenobarbital, “milk of amnesia” or propofol, used as a mild anesthetic for procedures like colonoscopies, as well as fentanyl for pain.
“If you look at the list, there’s a good chance you’re going to know somebody who’s on one of these medications,” said Vrana.
Matt Stripp, director of toxicology at Allegheny Health Network and an emergency department physician, said no “classic interactions” with cannabis came to mind in terms of patients visiting ERs, but he does frequently see patients with cannabis hyperemesis syndrome, or persistent vomiting from the drug.
“The cannabis-warfarin link is well-documented, but I’m not sure I’ve ever seen it,” he said.
He speculated that could be from underreporting and a lasting stigma to disclose using cannabis to physicians.
“It’s important to recognize that cannabis has historically been an illicit substance, so there are not a huge number of studies looking at this,” he said. “Maybe there are more unintended consequences than we know of.”
Cannabis also contains hundreds of different compounds, and researchers are still parsing out the effects of them both separately and together on the body. So identifying one specific cannabis compound or interaction that may have led to an ER patients’ symptoms can be “a bit of a mixed bag,” he said.
And while alcohol does not directly interact with cannabis in the same way the aforementioned drugs do, it enhances the sedative effects of cannabis, being a sedative itself. This can add to feelings of sleepiness or sedation, which people who choose to mix them should note.
One study found that for adverse drug events that led to emergency room visits, more than half were considered preventable, and were linked to drug interactions, like mixing too many drugs or taking two drugs that had the same effect.
“Pointing out that drug interactions exist with cannabis can put it on people’s radars,” said Stripp. “People tend to think cannabis is not a drug, so they don’t need to list it as one.”
To reduce the risk of this happening, experts encourage people to disclose what they’re taking to their physicians: including recreational substances and herbal supplements.
“From a public health standpoint, it’s important that people get over the stigma of using cannabis,” said Vrana. “People don’t think to say, ‘I’m using CBD oil to help with whatever.’ And that disclosure is important, because the molecule itself is not harmful, but it interferes with the metabolism of your prescription drugs. And so it’s vitally important that folks let their doctors know what they’re taking, and everything they’re taking. Just because it’s natural does not mean it’s safe.”
H/T: www.post-gazette.com
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