What You Need to Know About CBD Side Effects
Expert answers to your top questions about how to safely use CBD for maximum health benefits.
CBD products—made from a chemical found in the cannabis plant called cannabidiol—are all the rage right now. You can buy them online, in drugstores, and even at local gas stations, not to mention at medical marijuana dispensaries. While companies make some broad claims about what CBD can do, the truth is that there just isn’t a lot of definitive scientific evidence on this yet. Here’s the current body of knowledge on CBD’s side effects and how effective it is in treating things like chronic pain, anxiety, and sleep problems.
How Your Body Reacts to CBD
First of all, the only CBD that’s approved by the U.S. Food and Drug Administration (FDA) is Epidiolex, a seizure medication for kids with rare seizure disorders. Because of this, most of what we know about CBD side effects comes from the clinical trials for Epidiolex. In those trials, the most common side effects were drowsiness, decreased appetite, diarrhea, fatigue, elevated liver enzymes, rash, insomnia, and infections.
However, “that can’t necessarily be generalized to the larger population,” says Ryan Vandrey, Ph.D., a professor in the Behavioral Pharmacology Research Unit at Johns Hopkins University School of Medicine in Baltimore. “The kids in those trials were usually taking a lot of other medications, so the adverse events seen won’t necessarily translate to a healthy adult.” They were also taking extremely high doses of Epidiolex, much more than a typical person uses for anxiety or pain.
CBD that you buy at the drugstore and CBD you get at a medical marijuana dispensary are not the same either, which means the side effects could be different, points out Maureen Leehey, M.D., director of the Movement Disorders Division at the University of Colorado School of Medicine in Denver, CO. CBD purchased from a dispensary contains more tetrahydrocannabinol (THC), the chemical that causes a high, than CBD you can get from other outlets. Why? Because each kind is extracted from two different types of cannabis plants—hemp or marijuana.
Typically, at a medical marijuana dispensary, you’ll find CBD that has been extracted from a marijuana plant, which means it has more than 0.3% THC, rather than hemp, which contains 0.3% or less THC. But even if you buy a CBD product made from hemp, since the amount of THC in CBD is poorly regulated, there may be a lot more in your product than you think, Dr. Leehey says. All this means that you could experience side effects from THC rather than CBD, depending on what you’re using.
Then there’s the matter of dosage differences. You might be taking 5, 10, or 20 mg of CBD at a time, whereas someone on Epidiolex takes up to 20 mg/day per kg of body weight (this translates to 1360 mg/day for a 150 lb. person). That said, Dr. Leehey says CBD in these low doses tends to be very well tolerated and have few side effects.
How CBD Interacts With Your Meds
CBD has the potential to interact with other drugs, which can lead to some serious side effects. “We don’t have a full knowledge of the extent of those interactions at this point,” Vandrey says, “but it does seem that CBD will impact the metabolism of several other classes of drugs.”
The Epidiolex trials showed significant drug interactions, according to Dr. Leehey. Because CBD is metabolized by the liver, it tends to interfere with other medications that are also metabolized by the liver, like certain antidepressants, blood thinners, benzodiazepines, and other seizure medications.
“There are two particular liver enzymes that CBD will act through, so if another drug you’re taking is also working through those enzymes, that drug might be more or less potent,” she explains. The same is true for how these liver-metabolized drugs affect CBD—they can make CBD more or less potent.
Both experts agree that it’s important to talk to your doctor before you use CBD, especially if you’re taking other medications, because there is such a high potential for drug interactions.
But Does It Work?
Most of what we know about how effective CBD is for treating chronic pain and helping with sleep is anecdotal, says Vandrey. “It’s possible that it does help, but we need evidence that it does,” he says. Vandrey also believes that when it comes to pain relief, “we need to understand whether it’s CBD or some other substance in these CBD preparations that’s helping with pain.” For instance, he says a lot of the topical CBD formulations on the market contain the same active ingredients as other topical pain relievers, such as lidocaine, menthol, camphor, salicylates, or capsaicin, found in products like Icy Hot, Biofreeze, Capzasin, and Bengay. “While I don’t doubt that people who report pain relief are experiencing pain relief, it may be due to the formulation of that particular product and possibly independent of CBD,” Vandrey says.
And while some studies have found that CBD can significantly reduce social anxiety, “beyond that, we’re still lacking good quality data on evaluating its impact on anxiety,” Vandrey says. Without the robust research to support it, Dr. Leehey doesn’t recommend using CBD for anxiety or sleep, plus she says they’re expensive for what you get out of them. But if you’re still curious about giving CBD a try, here’s what Dr. Leehey says to look for:
For sleep, try a CBD product made from hemp or a high CBD-low THC product from a dispensary. (The THC content shouldn’t be more than 1–2 mg and the CBD should be around 10 mg, she says.) Take it before bed for 10 days and see if it helps. If not, discontinue.
If you want to try CBD for anxiety, consider progressively increasing your dose over the course of a month (one dose lasts around 6–8 hours). Start with 5 mg of a CBD oil or gummy twice a day for a few days, then go up to 10 mg twice a day. After that, try 10 mg three times a day, slowly building up to a maximum of 25 mg three times a day over the month. Stay on that maximum dose for another month and see if it’s beneficial. If it’s not helping, cut your dose in half for a week, then cut it in half again for a week, and then stop.
Proceed With Caution
Dr. Leehey says older people should be careful when taking THC because it can cause dizziness, increasing the risk for falls. And if you have psychosis, anxiety, depression, or epilepsy, it’s probably best to avoid THC too. Basically, “if you want to take CBD for your medical condition, talk to your primary care physician or a medical marijuana doctor first,” Dr. Leehey advises.
Remember that Epidiolex is the only CBD product that’s approved by the FDA, and it’s available only by prescription, says Vandrey. “Anything purchased outside of that FDA-approved product comes with risks. And the quality assurance is questionable for a lot of these products.”
There are studies, including ones Vandrey has been involved with, that repeatedly show dosing accuracy on CBD product labels is not very good. These studies have found that many products also contain contaminants like heavy metals, pesticides, and even other drugs. “You have to be a little bit worried about what you’re getting from a quality perspective, as well as from a dose accuracy perspective,” he says.
The safety and efficacy claims about CBD products may also be overstated right now. “I’m not saying they’re not safe, I’m not saying they’re not effective, what I’m saying is that any time you evaluate safety or efficacy, it has to be done for a specific product,” says Vandrey.” In other words, while Epidiolex has been evaluated for safety and efficacy, this doesn’t mean all CBD products work the same way, or even contain the same amount of CBD.
For example, researchers in one study Vandrey participated in purchased 84 CBD products online that supposedly had the same amount of CBD in them. They found that 26% of the products had less CBD in them than their labels claimed, 43% had more CBD, and only 31% had the amount of CBD the label indicated.
Bottom line: If you decide you want to try CBD products, even if you don’t have a specific health condition, it’s a good idea to talk to your doctor first. This especially applies if you’re taking other medications, including over-the-counter drugs or supplements. Your pharmacist is also a good resource for finding out about potential drug interactions. It’s best to be zealous when it comes to your health.
Epidiolex Trial Side Effects: Epidiolex (cannabidiol). (2020.) “Highlights of Prescribing Information: Adverse Reactions: Clinical Trials Experience.” epidiolex.com/sites/default/files/pdfs/1120/EPX-03645-1120_EPIDIOLEX_(cannabidiol)_USPI.pdf
CBD Side Effects: Mayo Clinic. (2020.) “Marijuana: Safety and side effects.” [mayoclinic.org/drugs-supplements-marijuana/art-20364974
THC Side Effects: Mayo Clinic. (2020.) “What are the benefits of CBD—and is it safe to use?” mayoclinic.org/healthy-lifestyle/consumer-health/expert-answers/is-cbd-safe-and-effective/faq-20446700#v
Topical Pain Relievers: Mayo Clinic. (2019.) “Arthritis pain: Treatments absorbed through your skin.” mayoclinic.org/diseases-conditions/osteoarthritis/in-depth/pain-medications/art-20045899