One common question beginners or new CBD users ask is “What are the side effects of CBD?”
Although CBD appears to be a safer alternative to many prescription medications — especially for difficult-to-treat conditions such as rare types of epilepsy — it’s not a silver bullet with zero downsides.
CBD can indeed cause some negative side effects. However, they’re considered mild, especially when compared to those caused by many pharmaceutical drugs.
Here’s what we know about CBD’s side effects, drug interactions, and other safety-related concerns.
Short Term Side Effects of CBD Oil
Studies using high doses of CBD oil in humans have reported several mild-to-moderate, short-term side effects, including: ¹
Tiredness
Drowsiness
Diarrhea
Dry mouth
Low blood pressure
Lightheadedness
Changes in appetite or weight
However, it’s important to be aware that research studies are not an accurate representation of real-world CBD use. Researchers tend to utilize a pure form of CBD called CBD isolate and administer it orally for 4 weeks or longer in very high daily doses of 300 mg or more.
In comparison, most people take CBD in much smaller doses (20–100 mg daily) and use CBD oil tinctures rather than capsules or other ingested products.
Many also use products containing full-spectrum hemp extract, rather than purified CBD, which contains not only CBD but other cannabinoids, terpenes, and various hemp compounds.
Research evidence shows that full-spectrum CBD preparations cause fewer side effects than purified CBD, which they think may be due to requiring smaller doses for similar therapeutic outcomes. The higher potency of full-spectrum CBD is speculated to be from the synergy between the plant’s many components, what researchers call the “entourage effect”. ²
The bottom line is that the side effects mentioned above are likely to be mild.
Furthermore, they have a low chance of occurring for most CBD users.
Side Effects of Full-Spectrum CBD Products
As we mentioned above, some CBD oil products are made with full-spectrum hemp extract, which means they contain not only CBD but many other compounds.
In particular, full-spectrum CBD can contain up to 0.3% of THC, the cannabinoid largely responsible for the mind-altering “high” associated with cannabis.
This amount of THC is not enough to cause intoxication in the vast majority of people. Having said that, some individuals are so sensitive to THC that they may experience unwanted effects by taking a large enough dose of a full-spectrum CBD product.
The potential side effects of full-spectrum CBD include feelings of anxiety or paranoia. Nonetheless, these effects are unlikely to occur for most individuals.
Long Term Side Effects of CBD Oil
CBD does not appear to cause any long-term side effects in humans. More importantly, there’s no evidence that you can become dependent on CBD, develop a tolerance to its effects, or have withdrawal symptoms if you stop taking it after prolonged use.
That’s another major advantage over some prescription medications, such as opioid painkillers, which are notorious for their addictive properties.
In fact, studies are suggesting that CBD might help people reduce their usage of opioids and other addictive drugs, ³ making it a realistic option for tackling the opioid epidemic. Not to mention, cannabis and its many cannabinoids have been found to help reduce pain levels similarly to opioids.
Having said that, most studies of CBD had a duration of 4-6 weeks, so more data about its long-term effects — after months or years of daily usage — is needed.
CBD Oil Side Effects on Kidneys
So far, research has not revealed any side effects of CBD oil on the kidneys in healthy individuals. If anything, it may actually be beneficial in treating symptoms of advanced chronic kidney disease including pain and reducing the need for opioids. ⁴
One study on mice also showed that pure CBD reduced inflammation and protected kidneys from damage caused by the chemotherapy drug cisplatin. ⁵
Is CBD Oil Bad for Your Liver?
The Food and Drug Administration (FDA) has raised concerns over the safety of CBD because of the belief that it can cause liver injury. However, this claim is based largely on a single study done in mice.
In this 2019 study, mice were given varying doses of CBD either acutely (one time) or for 10 days. The doses ranged from 61.5 to 2460 mg/kg. This means that at the highest dosage, mice were given almost 2.5 grams of CBD for every kilogram of body weight.
In the acute experiment, only a CBD dose of 2460 mg/kg produced signs of liver toxicity. This dose is equivalent to about 200 mg/kg for humans. The researchers found similar signs of liver damage in mice given 615 mg/kg (equivalent to 50 mg/kg in humans) of CBD for 10 days.
They concluded that “CBD exhibited clear signs of hepatotoxicity [liver toxicity].”
But acknowledged that the high doses required for such an outcome are not applicable to most real-world scenarios. ⁶
The average body weight worldwide is 62 kg. ⁷ Using the equivalent doses suggested by the study, this means the average person would have to take 12,400 mg (12.4 grams) of CBD at once or 3,100 mg (3.1 grams) for at least three days to experience liver damage.
These doses are nowhere near the 20–100 mg taken by CBD users.
In sum, there isn’t any evidence to suggest that CBD is bad for your liver unless you’re taking ridiculously large doses.
CBD & Fertility
Some people wonder if CBD has any effects on fertility. Thus far, there’s very limited evidence to indicate whether CBD has any significant impact on fertility in humans.
The only thing we know for certain is that taking CBD at the commonly recommended doses doesn’t seem to have any serious negative effects on the reproductive system in healthy individuals.
One 2018 study did show that male mice given CBD (15 or 30mg/kg) for 34 days straight had a 30% reduction in fertility rate. ⁸ A similar 1987 study reported that CBD reduced the fertility of sea urchin sperm. ⁹
However, these kinds of findings need to be confirmed by human studies before we can say anything conclusive.
Can You Be Allergic to CBD?
It’s highly unlikely to experience an allergic reaction to CBD itself. Scientific studies have not reported any evidence of CBD allergies. On the contrary, research on mice suggests that CBD may help with certain allergic responses by reducing inflammation. ¹⁰
Nonetheless, it’s possible to have an allergic reaction to other ingredients present in CBD products. One likely culprit is terpenes — natural aromatic compounds present in many CBD oils and other CBD products.
For example, one 2017 study found that some people had an allergic reaction when their skin came in contact with limonene or linalool, two common cannabis terpenes. ¹¹ There’s also some evidence that certain terpenes can be irritating to the skin, eyes, and mucous membranes. ¹²
Another possible allergic ingredient is cannabis pollen, the powdery substance produced by male cannabis plants. However, pollen is unlikely to find its way into cannabis products because male plants are not widely used in cannabis cultivation.
This is even more true for hemp-derived CBD products because CBD is usually used in the form of an oil, an extract that doesn’t contain any plant parts.
Finally, some CBD products — especially topicals — can also contain many other ingredients that can potentially cause allergic reactions, such as fragrances and preservatives.
Vaping CBD Side Effects
Vaping CBD can cause all of the same short-term side effects we discussed earlier. However, the real question is whether vaping CBD — or anything else, for that matter — is safe.
For instance, one study found that higher doses of propylene glycol and vegetable glycerin — the two most common ingredients in vape e-liquids, including those containing CBD — were toxic to cells. ¹³
Another study reported that e-cigarettes can produce acetaldehyde, acrolein, and formaldehyde, three toxic compounds that contribute to cardiovascular and lung disease while a 2019 paper found that e-cigarettes are associated with an increased risk of a heart attack. ¹⁴ ¹⁵
Finally, a comprehensive report by the National Academies of Science, Engineering, and Medicine looked at the findings of dozens of studies.
They found that there’s conclusive evidence that vaping products can produce multiple potentially harmful substances, as well as substantial-to-moderate evidence that vaping carries other risks and can increase coughing, wheezing, and asthma attacks.
The dangers of vaping were highlighted by the recent outbreak (from March 2019 to February 2020) of vaping-related lung injury in the US, where 2,800 people were hospitalized and 68 died. ¹⁶
Although this outbreak was largely linked to products containing vitamin E acetate, it still highlights the fact that inhaling anything other than air is likely detrimental to your health.
CBD Drugs Interactions
CBD can interact with many prescription drugs by altering the function of certain enzymes and proteins. These natural molecules are involved in metabolizing (breaking down) a wide variety of prescription medications.
As a result, CBD can drastically change the effects of many drugs.
CYP450 Enzyme Inhibition
Some studies have reported that CBD can suppress the activity of cytochrome P450 enzymes. ¹⁷ This enzyme family is abundant in the liver, where it helps metabolize the majority of prescription drugs.
Taking CBD alongside these medications can change how they are metabolized by the liver, which can modify their intended effects. Just some of the prescriptions whose effects CBD may alter include:
Theophylline, used for respiratory conditions
Chlorzoxazone, a muscle relaxer used for treating pain
Amitriptyline, an antidepressant
Ondansetron, used to relieve nausea and vomiting caused by surgery or cancer treatment
Clozapine, used to treat schizophrenia
The complete list involves dozens of common prescriptions used for every kind of health disorder.
At the same time, this also means that many medications can affect CBD’s metabolism by interacting with the same enzymes, lowering or increasing the concentration of CBD in the blood.
p-Glycoprotein Inhibition
CBD can also interact with medications by inhibiting P-glycoprotein. ¹⁸ This protein helps transport various drugs in and out of cells, which means CBD can have a significant impact on their effects.
P-glycoprotein helps the body utilize many drugs, including HIV antivirals, epilepsy and chemotherapy medications, antihypertensive drugs, immunosuppressants, blood thinners, and steroids. ¹⁹
Some drugs, such as the immunosuppressant cyclosporin, interact with both P-glycoprotein and CYP450 enzymes, which means CBD can have an even bigger impact on their effects.
The bottom line is that more research needs to be done to identify CBD’s precise impact on specific medications and anyone taking prescription drugs should talk to their doctor before using CBD.
Current FDA Stance on CBD Safety
The FDA is taking a “better safe than sorry” approach towards CBD, claiming that there’s insufficient research to broadly label it a fully safe substance. The organization argues that CBD may:
cause side effects
cause liver injury
affect other medications people take
be dangerous when taken alongside other substances that slow brain activity, such as alcohol
harm male fertility
Although their areas of concern are backed by a wide range of research findings, many of them are from preliminary studies conducted on animals that don’t use common real-world doses of CBD.
The FDA also stresses that we don’t know enough about CBD’s safety in specific situations, such as a growing fetus, the developing brains of children, or taking it daily for a prolonged period of time.
Should You Be Concerned About CBD’s Side Effects?
This list of CBD’s potential negative side effects can undoubtedly sound scary, but remember the popular saying: “The dose makes the poison.”
Taken at normal dosages, CBD offers relief with minimal side effects for most people.
Generally speaking, it’s only when individuals take extremely high CBD doses — such as those used for treatment-resistant epilepsy — that side effects become a more serious concern.
For the average healthy person, there isn’t much to worry about when you use CBD, especially in combination with a healthy diet, lifestyle, and exercise regimen.
Besides, CBD is a far safer alternative to many prescription drugs, whose effects can be worse than the issue they’re treating.
Nonetheless, it’s important to stress that although CBD has an excellent and well-documented safety profile backed by decades of studies, we don’t yet know everything about its effects.
That’s why you should always consult with your healthcare provider before using CBD, especially if you are currently on a prescription.
Gleb Oleinik is a freelance CBD & cannabis writer from Vancouver, Canada. He’s read thousands of studies about cannabinoids and other beneficial natural compounds, helping him translate complex science into plain language. He’s also written third-party lab test reports of CBD products and knows the industry inside and out. When he’s not writing, Gleb likes to spend his time in the gym and out in nature.
Frequently Asked Questions
CBD hemp oil can cause minor side effects, including tiredness, drowsiness, diarrhea, dry mouth, low blood pressure, and changes in appetite or weight. However, these effects have only been reported in studies using large doses of pure CBD.
CBD oil doesn’t have any severe side effects. However, it can amplify or reduce the effectiveness of many drugs, which is why it’s imperative to consult your doctor before using it if you’re taking any prescription.
Water-soluble hemp oil containing CBD doesn’t have any additional side effects over regular CBD oil.
