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.
People considering or taking CBD products should always mention their use to their doctor, particularly if they are taking other medications or have underlying medical conditions, such as liver disease, kidney disease, epilepsy, heart issues, a weakened immune system, or are on medications that can weaken the immune system (such as cancer medications). A pharmacist is a great resource to help you learn about a potential interaction with a supplement, an herbal product (many of which have their own drug interactions), or an over-the-counter or prescription medication. Don’t assume that just because something is natural, it is safe and trying it won’t hurt. It very well might.
Doubling up on side effects
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.
Researchers from Penn State College of Medicine evaluated existing information on five prescription CBD and delta-9-tetrahydrocannabinol (THC) cannabinoid medications: antinausea medications used during cancer treatment (Marinol, Syndros, Cesamet); a medication used primarily for muscle spasms in multiple sclerosis (Sativex, which is not currently available in the US, but available in other countries); and an antiseizure medication (Epidiolex). Overall, the researchers identified 139 medications that may be affected by cannabinoids. This list was further narrowed to 57 medications, for which altered concentration can be dangerous. The list contains a variety of drugs from heart medications to antibiotics, although not all the drugs on the list may be affected by CBD-only products (some are only affected by THC). Potentially serious drug interactions with CBD included
The researchers further warned that while the list may be used as a starting point to identify potential drug interactions with marijuana or CBD oil, plant-derived cannabinoid products may deliver highly variable cannabinoid concentrations (unlike the FDA-regulated prescription cannabinoid medications previously mentioned), and may contain many other compounds that can increase the risk of unintended drug interactions.
As a doctor who considers prescribing cannabis or a patient wishing to try CBD or medicinal cannabis, you need to be aware of how the cannabinoids might interact with other medications in the body.
Caution is also advised when prescribing cannabis to people who are in therapy with sedative-hypnotics like barbiturates or benzodiazepines. This also includes other psychoactive drugs with an effect on the central nervous system. Cannabis has the potential to have an additive or synergistic effect with these drugs which can cause severe drowsiness, dizziness and other unwanted side-effects(3).
Cannabis Drug Interactions – How Does THC and CBD Interact with Other Medicines?
It is essential always to think carefully before initiating cannabis treatment and to monitor patients closely who have a history of unstable cardiovascular disease, myocardial infarction or stroke. If you are a doctor who has a patient on anticoagulant medications whom you know, or suspect uses cannabis, it might be worth bringing up this risk.
Delta-9-tetrahydrocannabinol, also known as THC, may inhibit cytochrome P450 enzyme CYP2C9, which is responsible for metabolising Warfarin, a blood thinner used for people who receive new heart valves, among others. This can cause the INR (elevated international normalisation ratio), a measurement of the time it takes the blood to clot to go up, which in turn can cause internal bleeding(1).
Cannabidiol (CBD) has been shown to inhibit the CYP2C19, which is responsible for converting clopidogrel to its active thiol metabolite. Clopidogrel is often given to people who had a heart attack (myocardial infarction) or a cerebral stroke. Since CBD can block the activity of CYP2C19, it has the potential to lead to sub-therapeutic levels of the active metabolite and consequently an elevated risk of stroke(2).