CBD oil is believed to be generally safe and well-tolerated, but it is not free of side effects. Read on to learn which adverse effects you should watch out for when using CBD oil, how the delivery form influences them, and what you can do to reduce your risk.
CBD Oil Side Effects
First, it is important to remember that CBD oil is considered experimental and investigational and far more clinical studies are needed before we can make any firm conclusions about its supposed benefits [1].
Similarly, it’s an insufficiently investigated supplement with a relatively unknown safety profile. The list of side effects listed in this article is, therefore, not a definite one.
So, make sure to speak with your doctor before starting on a CBD oil regimen.
With the recent legalization of CBD oil in many states worldwide, its popularity is booming and people are taking it for not only its FDA-approved use for seizures, but also conditions such as [2]:
An advantage of CBD oil is that it’s considered generally safer and causes fewer adverse effects than the drugs typically used for these conditions. Chronic doses of up to 1500 mg/day were tolerated well in multiple studies [3+, 4].
Unlike THC, CBD doesn’t cause behavioral and psychological side effects. What’s more, it may even reduce some of them such as anxiety, psychosis, and memory loss [5, 6, 7, 8].
Nevertheless, there are some potential side effects of CBD oil that you should watch out for. Below is a detailed overview of the most common ones.
1) Dry Mouth
Whether you use them for recreational or medicinal purposes, cannabis products will often make your mouth feel as if it were stuffed with cotton balls. Almost 12% of 1500 people responding to a survey about CBD use experienced dry mouth, making it the most common adverse effect [2].
Stimulation of the CB1 and CB2 receptors in the salivary glands reduces saliva secretion, which makes the mouth feel dry. The well-known cannabis compound THC activates these receptors directly. In turn, CBD raises the levels of an activator naturally produced in the body – the cannabinoid anandamide [9, 10, 11, 12].
2) Digestive Issues
Both CBD oil supplements and the FDA-approved CBD medicine Epidiolex have been reported to cause digestive issues such as [2, 4]:
- Nausea and vomiting
- Diarrhea
- Increased or reduced appetite
- Weight loss or gain
Because preliminary research suggests that CBD improves rather than causes nausea and diarrhea, these effects most likely result from the irritating effects of other ingredients (e.g., carrier oils) on the bowels [13, 14, 15].
Alternatively, the loose regulation of supplements may allow for excessive CBD levels in products or harmful contaminants such as pesticides, heavy metals, and solvents [16+, 17].
In turn, the endocannabinoid system has a role in promoting appetite. The mixed effects of CBD on appetite and weight seen in different studies may be due to its dual effect: it blocks the CB1 and CB2 receptors but boosts the levels of their activator anandamide [18, 19, 11].
If you experience digestive issues from using CBD oil, tell your doctor. He or she may recommend reducing the dose or shifting to another brand.
3) Drowsiness and Fatigue
People taking CBD oil often report feeling sleepy and tired. Indeed, this side effect was observed in early clinical trials and one of the most common uses of CBD oil is to improve sleep disorders [20+].
If the symptoms are very severe, you shouldn’t drive or operate heavy machinery.
The effect of CBD on sleep seems to be biphasic: high doses may increase sleeping time, lower amounts may promote wakefulness. Additionally, levels of endocannabinoid receptors depend on the circadian rhythm. This may explain why CBD tends to cause drowsiness later in the day but has the opposite effect in the morning [21, 22, 23].
4) Dizziness
High doses of CBD lowered blood pressure in a small trial on 9 people. In turn, THC seems to have a more complex effect: it slightly raises blood pressure in people lying down but increases the risk of sudden blood pressure drops when standing up [24, 25+].
As a result, a common adverse effect of CBD – both alone and with equal amounts of THC (nabiximols) – is feeling dizzy and light-headed [26, 27, 28].
If your blood pressure drops too much, you may faint. The risk is especially high in people diagnosed with low blood pressure or on blood pressure medications – such as diuretics, ACE inhibitors, and beta-blockers. These people should be especially cautious with CBD oil and never try it out without discussing it with their doctor.
5) Possible Liver Damage
Several trials testing CBD for seizures found possible liver damage (high transaminases ALT and AST) in 9-25% of the people. The risk increased with the dose and was highest in people also taking the anti-seizure drug valproate, which is known to cause liver injuries [29+, 30, 31, 32, 33, 34].
Similarly, CBD caused signs of liver toxicity (high transaminases, alkaline phosphatase, and bilirubin) in mice and dogs. However, the doses were generally higher than those used in human trials [35, 36, 37].
Make sure to talk to your doctor, especially if you are taking valproate, and never exceed the recommended CBD oil dose to reduce your risk of liver damage.
6) Irritability
CBD is often used to curb anxiety, although research suggests it has “inverted U-shaped” effects: moderate doses, but not low or high amounts, may be effective for a range of anxiety disorders and stressful situations [38, 39].
In contrast, very high doses may even trigger anxiety and irritability. This was the case in 7-9% of the children in 2 clinical trials using CBD for seizures and autism [40, 41].
The effect probably involves the TRPV1 receptor, the activation of which increases the brain’s response to stressful situations [42].
CBD boosts the naturally-produced cannabinoid anandamide. While moderate anandamide levels activate CB1 receptors and curb anxiety, high amounts may worsen it by binding to TRPV1. CBD also activates this receptor directly, further contributing to the potential anxiety-triggering effects [43, 44, 11, 45].
7) Immune Suppression
CBD may reduce the immune response. It prevents T cells from dividing, migrating to inflammation sites, and producing pro-inflammatory cytokines. This may be beneficial in people with autoimmune conditions such as rheumatoid arthritis or multiple sclerosis [46, 47, 48, 49, 50, 51, 52].
The downside of blocking the immune response is that it may make people with weakened immune systems more prone to infections. Thus, people on immunosuppressants or with conditions such as HIV, diabetes, and Down syndrome might want to avoid it [53].
Kidney Health
CBD didn’t damage the kidneys in clinical trials. In fact, researchers believed it protected against kidney injury and inflammation in numerous animal studies [54, 55, 56, 57, 58]. Remember that larger and better designed clinical trials are needed before these findings are conclusive.
Though more clinical trials are needed, the current evidence suggests CBD oil will not harm your kidneys at normal doses.
On the other hand, people with kidney disease should probably avoid THC-containing medical marijuana without consulting a doctor.
According to a recent review, THC may worsen kidney health and increase urination by activating CB1 receptors. Remember that, unlike THC, CBD blocks these receptors. However, CBD may indirectly activate them by increasing anandamide levels in the body [59+].
Lastly, avoid synthetic cannabinoids at all costs (products like “spice” and “K2” sold in smoke shops). These chemicals caused sudden and severe kidney injury in several cases [59+].
Are You at Risk of CBD Oil Side Effects?
Risk Populations
CBD altered the levels of two drug transporters in placental cells. This suggests that taking CBD oil during pregnancy may increase the exposure of the fetus to any drugs that the mother takes. Pregnant women should avoid CBD oil in any case, since safety data are lacking [60].
Taking THC-containing CBD oil during pregnancy and breastfeeding is particularly dangerous, since THC may reduce growth and cause brain developmental anomalies in babies [61+].
Because there are no studies testing its safety in children below 2 years old, it’s better to avoid giving them CBD oil unless prescribed by a doctor.
CBD is thought to be safe in older children, but they may be more sensitive to THC and toxic contaminants such as heavy metals and pesticides than adults. Be sure to use high-quality, THC-free CBD in children and consult the doctor first.
Drug Interactions
Most drugs are broken down by liver enzymes. Among them, cytochrome (CYP) P450 plays a key role. A single CBD dose blocks several CYP enzymes, such as:
By doing so, it may slow the breakdown of several drugs and enhance their effects [62, 63, 64, 65, 66].
Indeed, CBD reduced the breakdown of the sedative hexobarbital, the anti-seizure drug clobazam, and the blood thinner warfarin in humans. It had the same effect on the immunosuppressant cyclosporin and the cannabis compound THC in cells [67, 68, 69, 70].
On the other hand, repeated CBD doses can increase the levels of some enzymes of this group and reduce the effects of the drugs they break down [71, 72, 73, 74].
Plus, CBD itself is broken down by CYP enzymes, especially by CYP34A and CYP2C19. Drugs that block these enzymes (such as ketoconazole and ritonavir) will enhance its effects, while those that activate them (such as phenobarbital and rifampicin) will have the opposite effect [75, 4].
If you are on prescription medication and plan to use CBD oil, ask your doctor about potential interactions and dose readjustment. Additionally, avoid combining CBD oil with grapefruit or other supplements that block the same liver enzymes (such as St John’s wort or watercress).
How Does the Delivery Form Influence CBD Oil Side Effects?
Oral
While rapid-release forms (mouth sprays and oil tinctures) deliver CBD directly into your bloodstream, slow-release forms (capsules, edibles, and teas) have to pass your digestive system first. This means their ingredients may irritate your bowels and give you nausea and diarrhea [76+, 77].
However, rapid-release forms will release CBD faster, so you may experience both wanted and unwanted effects sooner [76+, 77].
And since tinctures and sprays are directly applied in the mouth, they will quickly reach the salivary glands and cause dry mouth. Mouth sprays may also cause a stinging sensation and even burns, especially if they contain alcohol [9, 78].
Vapes
Vapes bypass the digestive system without irritating your bowels, but they may trigger the other adverse effects faster [76+, 77].
Vaping is considered safer than smoking cigarettes or joints because the oil is heated at lower temperatures that produce fewer toxic byproducts [76+ 79].
However, the additives used as flavorings and thinning agents in vaping oils may still pose some hazards. Although they are normally food-grade, they may release harmful compounds (including the cancer-causing formaldehyde) when vaporized. Their heavy use may lead to [80, 79, 81+]:
- Cough
- Dry throat
- Lung injury
- Fat particles entering the lungs (lipoid pneumonia – rare)
For instance, one man developed severe lung damage from vaping CBD oil [82+].
Creams & Gels
Creams and gels act locally on the application site and don’t release CBD into the gut or bloodstream. This means they will not cause most of the adverse effects previously described [76+].
However, they may cause allergic reactions with itching, redness, and rashes on the skin. It’s important to note that the reactions can be caused by either CBD or other ingredients in the formulation [83+, 84+].
How to Reduce Your Risk of Side Effects from CBD Oil
1) Drink More Water
The best way to reduce dry mouth when using CBD oil is to drink plenty of water and other hydrating liquids before, during, and after consumption.
2) Find Additive-Free Products
You can reduce the risk of digestive issues by choosing forms that bypass the gut and directly release CBD into your bloodstream such as vapes, mouth sprays, and oil tinctures. High-quality oils without additives may also irritate your bowels less.
3) Take it Before Sleep
If you feel drowsy or light-headed after taking CBD oil, you may need to reduce the dose or take it only before sleep.
4) Increase Wakefulness Naturally
Drinking coffee or tea will help you both stay awake and raise your blood pressure, but it also causes many side effects. Try to get more sunlight first thing in the morning, as it will energize you and help you get better sleep at night. We talk about other natural ways to increase wakefulness in this post.
5) Support Your Liver
Avoid combining CBD with the anti-seizure drug valproate. Additionally, make sure not to exceed the dose and regularly monitor your liver function to reduce your risk of liver damage. Eggs (choline), artichokes, NAC, and probiotics also support liver health. Read more foods and supplements that are good for the liver here.
6) Don’t Take Megadoses
Only very high CBD doses may cause irritability. Make sure not to exceed the dose and try reducing it if you notice this symptom.
7) Monitor Your Immune Response
If you have a weakened immune system, you should consult your doctor before taking CBD oil. You may need to avoid CBD or take a lower dose.
Additionally, you may also want to look into balancing your Th1/Th2 immune response. If you have a slightly weaker immune system and are prone to allergies, you are probably Th2-dominant.
Takeaway
Always make sure to speak with your physician before starting on a CBD oil regimen.
CBD oil is thought to be safe and most people seem to tolerate it well.
Low-quality products may contain additives and toxins that can irritate the lungs when vaped and the gut when taken orally. Choose high-quality products to reduce your risk.
Additionally, CBD oil can make you feel drowsy and lightheaded. If you feel tired after taking CBD oil, lower your dose or use it only before sleep. Look to also increase your wakefulness naturally by getting more sunlight during the day.
High doses may damage the liver, but likely only in people taking the anti-seizure medication valproate. Monitor your liver enzymes and look into natural ways to protect your liver.
Avoid CBD oil if you have a weak immune system, as it might make you more prone to infection.
If you take prescription drugs, consult your doctor. Many drugs can interact with CBD oil and increase the risk of side effects.
Pregnant women and children should avoid CBD oil until more safety data are available.
