A recent study suggests that medications’ effects can be diminished or negated by using marijuana.

Although some people may employ marijuana or cannabidiol to relieve aching joints or to help with sleep difficulties, it may be that such marijuana use may cause problems with their other medications’ effects. That’s because the same group of enzymes is used to process medications as well as marijuana products.

Researchers explained that the chemicals in marijuana, THC, cannabidiol (CBD), cannabinol (CBN), are metabolized in the body by at least two related groups of enzymes that also help process and eliminate more than 70% of prescription drugs most commonly used. This increases the risk that marijuana may dangerously intensify the effects of some prescription drugs or result in other drugs flushing through the system too quickly to exert any beneficial effect, according to lead researcher Philip Lazarus, PhD, a professor and chair of the department of pharmaceutical sciences at Washington State University in Spokane.

The researchers tested how pot chemicals might interfere with enzymes’ ability to break down other medications. They found that the major THC metabolites inhibited key enzymes, including several that play key roles in liver function. All three cannabis chemicals, but especially CBD, inhibited two of the primary liver enzymes. CBD was also found to block enzymes accounting for approximately 95% of kidney metabolism that helps clear toxins and some drugs from the body.

“We saw some significant inhibitions,” he said. “The concentrations we see in the lab are probably an indicator there is at least some inhibition of these enzymes in real time.” Some drugs that could be affected by marijuana use include pain killers such as acetaminophen (Tylenol) or ibuprofen (Motrin), blood thinners such as warfarin, and tamoxifen, the breast cancer drug, according to Lazarus.

“Adults—and patients in particular—have been consuming cannabinoids medicinally for centuries, and this practice has become quite commonplace over the past few decades,” said Paul Armentano, deputy director of NORML, an advocacy group favoring marijuana law reform. “Many of these patients are older and many of them may also be prescribed other medications. Were cannabinoids to be significantly contraindicated among this population, one would presume that there would be ample empirical evidence already available substantiating this concern.”

Lazarus explained that pot’s effects on the body’s metabolism would be unlikely to affect an individual who uses pot recreationally on weekends. “Even though it probably inhibits these enzymes, it doesn’t inhibit them enough to interfere with your everyday metabolism,” he said. The problem occurs as a result of mixing regular pot use with other drugs or taking marijuana-derived products along with prescription medications.

It’s important to discuss the use of marijuana products with your provider or pharmacist to ensure you’re not endangering your health through the use of cannabis-derived products in combination with prescription medications.