For decades, cannabis has topped the list of most used drugs, but with ongoing reforms including the legalisation of medical and even recreational cannabis, figures suggest that use of the drug is still on the incline. Patients in the UK and many other jurisdictions can now access cannabis-based medicines via prescription and, increasingly, casual consumers in countries such as the US and Canada can choose from an array of cannabis products at their local dispensaries. But while this improved access may have us believing that we can use cannabis in whichever way we choose, this isn’t always the case.
Like many drugs, cannabis derivatives such as CBD and THC can interact with other medications, resulting in undesirable, and sometimes dangerous, consequences. To avoid any potential side effects from mixing cannabis use – whether medicinal or recreational – with prescription medications, it’s a good idea to be aware of these interactions. So, with that in mind, we’re taking a look at some of the most common prescription drugs that don’t mix with cannabis.
Before using cannabis alongside prescription medications, it’s always recommended that you speak with your doctor. Understandably, many people recoil at the thought of such a conversation, especially if they aren’t able to access a prescription in the UK; however, your doctor may be able to offer you valuable advice regarding any potential drug-drug interactions. Nonetheless, we hope that this article will act as a rough guide as a first step.
How does cannabis interact with prescription drugs?
The intoxicating effects of cannabis – largely owing to the psychoactive compound, THC – are extremely well-known. However, research into this versatile plant remains underdeveloped. As a result, there is still a lot of uncertainty regarding not only how cannabis use affects our health and potentially aids in the treatment of various conditions, but also how it may change the effects of other drugs and medicines. But we are learning more.
A 2021 study, published in Drug Metabolism and Disposition, examined the interaction between three of the most common cannabinoids – cannabidiol (CBD), tetrahydrocannabinol (THC) and cannabinol (CBN) – and their metabolites, and liver and kidney enzymes. The UDP-glucuronosyltransferase (UGT) family of enzymes plays a central role in the metabolism and detoxification of a wide range of endogenous and exogenous compounds, including many pharmaceutical drugs.
The researchers of this study found that all three of the cannabinoids assessed demonstrated significant inhibition of these enzymes. This could lead to a build-up of these drugs in the body with potentially dangerous results. Their findings led the authors to conclude that cannabinoid exposure could play an important role in drug-drug interactions, as well as having “important implications in patients with impaired hepatic or kidney function.”
But which drugs, in particular, could pose a risk if taken in combination with cannabis or cannabinoids?
Anticoagulants, or blood thinners, are used to prevent blood clotting in the body. While there is little research into the effects of combining cannabis with blood thinners, one study found that CBD may compete with the anticoagulant, warfarin, at CYP450 enzymes which could prevent the body from breaking down the drug. This could lead to excessive bleeding or even overdose.
It is generally advised that patients don’t combine sedative medications, such as Ambien or Benadryl, with other sedative substances, including cannabis, as this could intensify the effects of the drugs. Furthermore, some evidence suggests that regular cannabis use is associated with the need for increased doses of sedatives. However, the specific reason for this is not completely understood.
A growing body of evidence suggests that combining medical cannabis with opioids could help patients achieve improved pain relief while reducing their opioid intake. However, combined use of cannabis and opioids could also have some negative side effects. For example, as both cannabis and opioids are known to suppress the central nervous system, combining the two could increase the risk of unwanted adverse effects such as lethargy and drowsiness.
Pain medications such as codeine, Percocet, and Vicodin, may also suppress the central nervous system and combination with cannabis could increase the risk of side effects. According to the NHS, combining cannabis use with painkillers such as codeine could put patients at an increased risk of serious side effects of codeine, including breathing difficulties, heart problems, having a fit or seizure, and even coma.
As always, solid evidence for how cannabis could interact with psychiatric medications such as anti-anxiety drugs and selective serotonin reuptake inhibitors (SSRIs) is still lacking. However, some evidence does suggest that combining cannabis with SSRIs could increase the risk of mania and serotonin syndrome (caused by a toxic influx of serotonin in the brain). This may be due to the inhibitory actions of CBD at specific enzymes.
Some medications can also increase or decrease the bioavailability of THC. Combination use could therefore either reduce or intensify the “high” you would usually experience from cannabis use alone. For example, some drugs that could increase the effects of THC include antidepressants, such as Fluoxetine, antimycotics, calcium antagonists, HIV protease inhibitors, proton pump inhibitors, such as Cimetidine, as well as Amiodarone and Isoniazid.
Combining cannabis with prescription drugs could have some significant and potentially harmful side effects. As previously stated, it is always recommended that you speak with your doctor about your cannabis use if you are currently, or are soon to be, taking any prescription – or even over-the-counter –medications. While the relative safety of cannabis as a drug on its own may make it easy to assume that it can be freely used with other medications, this is not always the case.