While generally considered safe, CBD may cause drowsiness, lightheadedness, nausea, diarrhea, dry mouth, and, in rare instances, damage to the liver. Taking CBD with other medications that have similar side effects may increase the risk of unwanted symptoms or toxicity. In other words, taking CBD at the same time with OTC or prescription medications and substances that cause sleepiness, such as opioids, benzodiazepines (such as Xanax or Ativan), antipsychotics, antidepressants, antihistamines (such as Benadryl), or alcohol may lead to increased sleepiness, fatigue, and possibly accidental falls and accidents when driving. Increased sedation and tiredness may also happen when using certain herbal supplements, such as kava, melatonin, and St. John’s wort. Taking CBD with stimulants (such as Adderall) may lead to decreased appetite, while taking it with the diabetes drug metformin or certain heartburn drugs (such as Prilosec) may increase the risk of diarrhea.
Many drugs are broken down by enzymes in the liver, and CBD may compete for or interfere with these enzymes, leading to too much or not enough of the drug in the body, called altered concentration. The altered concentration, in turn, may lead to the medication not working, or an increased risk of side effects. Such drug interactions are usually hard to predict but can cause unpleasant and sometimes serious problems.
Doubling up on side effects
Products containing cannabidiol (CBD) seem to be all the rage these days, promising relief from a wide range of maladies, from insomnia and hot flashes to chronic pain and seizures. Some of these claims have merit to them, while some of them are just hype. But it won’t hurt to try, right? Well, not so fast. CBD is a biologically active compound, and as such, it may also have unintended consequences. These include known side effects of CBD, but also unintended interactions with supplements, herbal products, and over-the-counter (OTC) and prescription medications.
Absolutely. Inhaled CBD gets into the blood the fastest, reaching high concentration within 30 minutes and increasing the risk of acute side effects. Edibles require longer time to absorb and are less likely to produce a high concentration peak, although they may eventually reach high enough levels to cause an issue or interact with other medications. Topical formulations, such as creams and lotions, may not absorb and get into the blood in sufficient amount to interact with other medications, although there is very little information on how much of CBD gets into the blood eventually. All of this is further complicated by the fact that none of these products are regulated or checked for purity, concentration, or safety.
CBD has the potential to interact with many other products, including over-the-counter medications, herbal products, and prescription medications. Some medications should never be taken with CBD; the use of other medications may need to be modified or reduced to prevent serious issues. The consequences of drug interactions also depend on many other factors, including the dose of CBD, the dose of another medication, and a person’s underlying health condition. Older adults are more susceptible to drug interactions because they often take multiple medications, and because of age-related physiological changes that affect how our bodies process medications.
“There is no role right now for CBD in managing mental disorders that I [treat], such as depression, bipolar disorder … anxiety and ADHD,” he says. “We just don’t have the evidence that supports [it].”
Are the concentrations in commercially available CBD high enough to cause this interaction? The evidence doesn’t really say one way or another. Dr. Alloway’s research involved a high dosage of CBD that wouldn’t be found in a retail product. However, it “highlights that a drug interaction is there,” she says. Plus, tacrolimus is metabolized in the body by a group of enzymes called cytochrome P450 and CBD is a known inhibitor of this process. What does that mean? If CBD inhibits the metabolism of tacrolimus, the patient can end up with too-high levels of tacrolimus in the body. In light of this, she urges anyone taking tacrolimus to speak with their transplant team before using CBD. Don’t get your hopes up, though—using herbal remedies, particularly those with potential interactions, is generally frowned upon by doctors looking after transplant recipients (including Dr. Alloway).
Dr. McIntrye, who co-authored a 2018 study that concluded that healthcare providers need more information about drug-drug interactions with CBD and psychotropic medication, says much of the information out there is confusing and contradictory. Therefore, he echoes Dr. Alloway’s statement that it is absolutely prudent that patients clear the use of CBD with their doctor before giving it a go.
Does CBD interact with medications?
While CBD is one of the active ingredients in marijuana, using CBD itself will not get you high (the component that does that is called tetrahydrocannabinol, or THC). CBD is really just a molecule within the hemp variety of the cannabis plant, and there is at least some anecdotal evidence and preliminary research suggesting that the extraction created from this molecule has some health benefits.
Case in point: tacrolimus , an immunosuppressive medication used to prevent organ rejection in patients who have had heart, liver, or kidney transplants. CBD interferes with the metabolism of tacrolimus, according to research conducted by Dr. Alloway , who specializes in post-transplant immunosuppression. And because tacrolimus is a narrow therapeutic index drug (meaning the window between efficacy and toxicity is very small), this interference can lead to clinically significant negative outcomes (such as kidney problems or organ rejection), she says.
As for other drugs, well, most haven’t been studied yet. There is preliminary evidence that CBD could have a similar effect to grapefruit juice, impairing how your body metabolizes drugs, and raising serum levels of those medications in your body. And, because cytochrome P450 is responsible for the metabolism of numerous medications , proceed with caution before mixing any prescription pharmaceutical with CBD, Dr. Alloway says.
But claims that CBD aids in the treatment of certain mental health and psychiatric conditions, don’t pass muster, says Roger McIntyre, MD , professor of psychiatry and pharmacology at the University of Toronto.
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