Cannabidiol (CBD): What we know and what we don't - Harvard Health (2025)

Cannabidiol (CBD): What we know and what we don't - Harvard Health (1)

Cannabidiol (CBD) is often covered in the media, and you may see it touted as an add-in booster to your post-workout smoothie or morning coffee. You can even buy a CBD-infused sports bra. But what exactly is CBD? And why is it so popular?

How is cannabidiol different from marijuana, cannabis, and hemp?

CBD, or cannabidiol, is the second most prevalent active ingredient in cannabis (marijuana). While CBD is an essential component of medical marijuana, it is derived directly from the hemp plant, a cousin of marijuana, or manufactured in a laboratory. One of hundreds of components in marijuana, CBD does not cause a high by itself.

According to a report from the World Health Organization, "In humans, CBD exhibits no effects indicative of any abuse or dependence potential…. To date, there is no evidence of public health related problems associated with the use of pure CBD." A recent study in the journal Neuropsychopharmacology concluded that "acute CBD alone is unlikely to significantly impair daily functioning or workplace performance."

Is cannabidiol legal?

CBD is readily obtainable in most parts of the United States, though its exact legal status has been in flux. All 50 states have laws legalizing CBD with varying degrees of restriction. In December 2015, the FDA eased the regulatory requirements to allow researchers to conduct CBD trials. In 2018, the Farm Bill made hemp legal in the United States, making it virtually impossible to keep CBD illegal — that would be like making oranges legal, but keeping orange juice illegal.

The Farm Bill removed all hemp-derived products, including CBD, from the Controlled Substances Act, which criminalizes the possession of drugs. In essence, this means that CBD is legal if it comes from hemp, but not if it comes from cannabis (marijuana) — even though it is the exact same molecule. Currently, many people obtain CBD online without a medical marijuana license, which is legal in most states.

The evidence for cannabidiol health benefits

CBD has been touted for a wide variety of health issues, but the strongest scientific evidence is for its effectiveness in treating some of the cruelest childhood epilepsy syndromes, such as Dravet syndrome and Lennox-Gastaut syndrome (LGS), which typically don't respond well to antiseizure medications. In numerous studies, CBD was able to reduce the number of seizures, and, in some cases, stop them altogether. Epidiolex, which primarily consists of CBD, is the first cannabis-derived medicine approved by the FDA for these conditions.

Animal studies, and self-reports or research in humans, suggest CBD may also help with:

  • Anxiety: Studies and clinical trials are exploring the common report that CBD can reduce anxiety.
  • Insomnia: Studies suggest that CBD may help with both falling asleep and staying asleep, in part by helping address chronic pain and anxiety.
  • Chronic pain: Increasingly, human studies are substantiating the claims that CBD helps control pain. One animal study from theEuropean Journal of Painsuggests CBD could help lower pain and inflammation due to arthritis when applied to skin. Other research identifies how CBD may inhibit inflammatory and neuropathic pain, which are difficult to treat.
  • Addiction: CBD can help lower cravings for tobacco and heroin under certain conditions, according to some research in humans. Animal models of addiction suggest it may also help lessen cravings for other addictive substances such as alcohol, cannabis, opiates, and stimulants.

Is CBD safe?

Side effects of CBD could include nausea, fatigue, and irritability. CBD can increase the level of blood thinning and other medicines in your blood by competing for the liver enzymes that break down these drugs. Grapefruit has a similar effect with certain medicines. This interaction is particularly important if you are taking a blood thinner, an anti-epileptic, or an immunosuppressant medication, all of which need to have stable levels in your blood.

People taking high doses of CBD may show abnormalities in liver-related blood tests. Many nonprescription drugs, such as acetaminophen (Tylenol), have this same effect. You should let your doctor know if you are regularly using CBD so that he or she can check your liver enzymes periodically.

A significant safety concern with CBD is that it is primarily marketed and sold as a supplement, not a medication. Currently, the FDA does not regulate the safety and purity of dietary supplements, and no one, really, is regulating the CBD market. So you cannot be sure that the product you buy has active ingredients at the dose listed on the label.

In addition, the product may contain other unknown elements. If you buy CBD, it is safest to make sure that there is independent laboratory testing as attested to by a COA (certificate of analysis) that should accompany every CBD product.

How can CBD be taken?

CBD comes in many forms, including oils, tinctures, capsules, patches, vapes, and topical preparations for use on skin. If you're hoping to reduce inflammation and relieve muscle and joint pain, a topical CBD-infused oil, lotion or cream — or even a bath bomb — may be the best option. Alternatively, a CBC patch or a tincture or spray designed to be placed under the tongue allows CBD to directly enter the bloodstream. Dcotors don't recommend smoking anything, including CBD.

Outside of the US, the prescription drug Sativex, which uses CBD as an active ingredient, is approved for muscle spasticity associated with multiple sclerosis and for cancer pain. Within the US, Epidiolex is approved for certain types of epilepsy and tuberous sclerosis.

The bottom line on cannabidiol

Some CBD manufacturers have come under government scrutiny for wild, indefensible claims, such that CBD is a cure-all for cancer or COVID-19, which it is not. We need more research, but CBD is proving to be a helpful, relatively non-toxic option for managing anxiety, insomnia, and chronic pain. Without sufficient high-quality evidence in human studies, we can't pinpoint effective doses, and because CBD currently is typically available as an unregulated supplement, it can be difficult to know exactly what you are getting, or to conduct studies.

If you decide to try CBD, make sure you are getting it from a reputable source. Again, please discuss your use of CBD or any other supplements with your doctor to make sure that it won't affect any other medicines you take.

Cannabidiol (CBD): What we know and what we don't - Harvard Health (2025)

FAQs

Is there any evidence that CBD works? ›

Published case reports and uncontrolled clinical trials suggest the potential of using CBD products for better sleep. In one unblinded study of 23 patients with epilepsy, 85% of those treated daily for three months with CBD showed an improvement in sleep.

What is one known side effect of using cannabidiol or CBD? ›

CBD use also carries some risks. Though it's often well-tolerated, CBD can cause side effects, such as dry mouth, diarrhea, reduced appetite, drowsiness and fatigue. CBD can also interact with other medications you're taking, such as blood thinners.

Do CBD gummies really relieve pain? ›

Animal studies have suggested that CBD has pain-relieving and anti-inflammatory properties, but these effects have not been validated in quality studies in humans. Anecdotally, some people with arthritis who have tried CBD report noticeable pain relief, sleep improvement and/or anxiety reduction.

What medications should not be taken with CBD? ›

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.

Is CBD proven to help anything? ›

CBD oil may help ease symptoms of anxiety, neurological disorders, heart health issues, and certain types of pain, among other health conditions. That said, while some study findings are available, more research is necessary to draw conclusions. Some studies are still ongoing.

Is CBD good or bad for the brain? ›

Several functional MRI (fMRI) studies investigated the effects of CBD on brain function in healthy individuals (Supplementary Table S1). Overall, CBD was found to reduce resting-state activity and connectivity across several brain regions, potentially indicating an anxiolytic (anxiety-reducing) effect.

Is CBD safe for the liver? ›

Cannabidiol (CBD) has gained popularity in the U.S. and Europe and is widely consumed and promoted to improve a variety of health conditions. Although safe for most, in rare instances, people receiving high daily doses of CBD can develop abnormalities in liver blood tests consistent with liver toxicity.

Are edibles safe for seniors? ›

Seniors should be aware of the potency of the edibles they consume and carefully read labels to understand the THC and CBD content per serving. Additionally, seniors should avoid consuming edibles on an empty stomach, as this can intensify the effects and increase the risk of adverse reactions.

Is CBD better than Viagra? ›

No, CBD gummies are not a replacement for Viagra. While CBD has potential health benefits, it has not been proven to be effective for treating erectile dysfunction (ED) in the same way as Viagra.

What is the strongest essential oil for pain? ›

Which Essential Oils Are Best For Pain? One of Mother nature's most powerful painkillers, peppermint oil is frequently used for alleviating pain [1]. Closely related to peppermint, wintergreen oil boasts similar properties due to its methyl salicylate component.

What does CBD oil do under your tongue? ›

Balance: CBD which is administered sublingually, bonds to the CB1 and CB2 receptors located under the tongue, and accesses regulatory systems like the nervous and immune systems. This means that the CBD oil is able to help the body maintain homeostasis.

How fast does CBD kick in for pain? ›

CBD onset time

Here's a look at how long it generally takes to feel the effects of different forms of CBD: Edibles: up to 2 hours. Tinctures sublingual sprays: 15 to 45 minutes. Topicals: 45 to 60 minutes.

What vitamins should not be taken with CBD? ›

There are no known interactions between CBD and vitamins. So, you can take them at the same time or at different times. In general, some space in between taking vitamins, CBD, medications or other supplements is ideal. This method gives your liver time to work on breaking down each compound individually.

Who shouldn't use CBD? ›

At least one animal study shows high doses of CBD can harm an unborn baby. Have liver disease: Studies show healthy people could get liver damage if they take high doses of the FDA-approved CBD drug, Epidiolex. People who already have liver problems may need to take a lower dose.

Can CBD cause high blood pressure? ›

A 2017 study of 9 male participants found that a single dose of CBD in healthy participants lowered blood pressure for people at rest and those who were under stress. Another 2017 study in mice found that CBD significantly reduced stress-induced increases in blood pressure and heart rate.

Is there evidence that CBD oil helps with anxiety? ›

Two studies from 1974 and 1982 found that CBD lowered anxiety caused by taking THC. A 1993 study found less anxiety in people who took CBD and then performed a public speaking test. People in a small study published in 2003 reported feeling less anxious after taking CBD than those who took a placebo.

Does the FDA recognize CBD? ›

These approved drug products are only available with a prescription from a licensed healthcare provider. Importantly, the FDA has not approved any other cannabis, cannabis-derived, or cannabidiol (CBD) products currently available on the market. Two well-known cannabinoids: Cannabidiol (CBD)

Does CBD make you feel spacey? ›

Frequently Asked Questions. To recap, here are the questions we are asked most commonly about CBD Oil: Does CBD Oil Make You Feel Spacey? No, CBD oil generally does not make you feel “spacey.” It is non-psychoactive, unlike its counterpart THC.

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