What to Know About CBD’s Effects on Prescription Medications


CBD’s Effects on Prescription Medications

According to experts at Harvard Medical School, cannabidiol (CBD) may be a therapeutic remedy for various conditions. However, experts also state that CBD interacts with other medications and may increase or decrease the effectiveness of some drugs. Here’s what you should know about taking CBD oil with other medicines.

Research Shows Interesting CBD-Drug Interactions in Animals

Much of the current research into CBD-drug interactions is based on animal studies. The research is not conclusive when it comes to the same interactions in humans. Far more research is needed with human subjects to know for sure how CBD affects drug levels in the body.

Animal studies aren’t as reliable as human studies due to the dosage methods and the concentrations of CBD administered. Human studies of drug interactions involve subjects who receive oral or inhaled CBD. 

CBD is administered orally or via injections in rodent test subjects. Blood plasma concentrations of CBD can vary widely between humans and rodents after oral CBD doses, and extra-large doses of injected CBD are often given to rodents to stimulate responses.

Both the injection of CBD in rodents and the wide differences between rodents and human CBD blood plasma levels mean that animal tests are unreliable in predicting whether humans will experience the same drug-interaction effects as rodents. 

In mice, CBD is more bioavailable, so the effects of CBD may be heightened in mice compared to CBD effects on humans.

Some Prescription Drugs Enhance or Block CBD-Metabolizing Enzymes

Several enzymes metabolize (make available to the body) CBD in humans. Three enzymes known to metabolize CBD are the CYP3A4, CYP2C9, and CYP2C19 enzymes. Other drugs suppress or enhance these enzymes, which can cause suppression of CBD effects or higher concentrations of CBD in the body.

Drugs that inhibit or block the CYP3A4 enzyme include the following:

  • Ketoconazol (Nizoral, Extina, Xolegel, Kuric)
  • Itraconazole (Sporanox)
  • Ritonavir (Norvir)
  • Clarithromycin (Biaxin, Biaxin Filmtab, Biaxin XL)

When a drug inhibits the CYP3A4 enzyme, CBD doesn’t degrade as fast in the system. The CBD levels in the body may be increased as a result and can remain active for a longer time than usual.

On the other end of the spectrum are drugs that enhance the CYP3A4 enzyme.

Drugs that induce CYP3A4 activity include the following:

  • Phenobarbital (Luminal, Solfoton, Mudrane, Antrocol, Bellergal, Lufyllin, Quadrinal)
  • Rifampicin (Rifamate, IsonaRif)
  • Carbamazepine (Carbatrol, Epitol, Equetro, Tegretol)
  • Phenytoin (Dilantin, Phenytek)

Drugs that induce the CYP3A4 enzyme may reduce the bioavailability of CBD in the human body. Dosages of CBD products may be too low to cause the desired therapeutic effects of CBD to be taken with CYP3A4 -inducing drugs.

Consumers should remember that most of the CYP3A4-related drug interactions were noted in animal studies using high concentrations of CBD administration. Human CBD-drug interactions may not be as obvious or impactful as the interactions found in animal subjects.

CBD Suppresses Some Drug-Metabolizing Enzymes

CBD can suppress the actions of drug-metabolizing enzymes in the body. For example, the enzyme that metabolizes hexobarbital (Evipan, Tobinal, Citopan) is inhibited by CBD. If you take a drug containing hexobarbital along with a CBD product, the concentration of hexobarbital may be increased in your system.

CBD may increase levels of the following drugs due to its inhibiting action on enzymes:

  • Macrolides
  • Calcium channel blockers
  • Benzodiazepines
  • Cyclosporine
  • Sildentafil
  • Antihistamines
  • Some statins

CBD studies have shown that warfarin levels (Coumadin, Jantoven) may be increased if you take warfarin while using CBD products. CBD also raises the levels of clobazam (Onfi, Sympazan) in children with epilepsy.

Research is ongoing for CBD’s Effects on Prescription Medications

The United States Drug Enforcement Administration (DEA) recently announced that regulations on hemp are being relaxed. Hemp is a species of cannabis that produces low levels of THC, which is the psychoactive component of cannabis.

Experts will continue to conduct additional research on hemp-derived CBD products to learn more about CBD-drug interactions. In the future, physicians and other health care providers can inform their patients about drug interactions based on extensive scientific research.

Until then, patients should always consult their health care providers about taking CBD products along with their prescription and over-the-counter medications. Consumers should also research the various CBD products and only purchase their CBD formulations from reputable suppliers.

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