Understanding Cannabidiol (CBD)
Cannabidiol, or CBD, is the second most prevalent active compound found in the cannabis plant [1.2.2]. Unlike tetrahydrocannabinol (THC), CBD is not intoxicating, meaning it doesn't produce a "high" [1.2.2]. It is available in many forms, including oils, supplements, foods, and lotions [1.2.5]. While the World Health Organization has stated that pure CBD does not seem to have abuse or dependence potential, its use is not without risks [1.2.2]. The only CBD product currently approved by the U.S. Food and Drug Administration (FDA) is a prescription oil called Epidiolex, used for treating specific seizure disorders [1.2.3, 1.6.2]. All other CBD products are largely unregulated, leading to concerns about purity, dosage, and unproven medical claims [1.3.3, 1.3.6]. A study of 84 CBD products purchased online revealed that over a quarter contained less CBD than indicated on the label [1.3.6].
Common Negative Side Effects of CBD
While often well-tolerated, CBD can cause several side effects. Clinical studies and user surveys have identified a range of common adverse reactions. Many of these effects are mild to moderate and may resolve when usage is stopped or the dose is reduced [1.2.6].
- Drowsiness and Fatigue: Somnolence (drowsiness or sleepiness) is one of the most frequently reported side effects. In clinical trials for Epidiolex, somnolence and sedation occurred in 32% of patients, a rate significantly higher than placebo [1.3.2]. This can affect daily functioning and make activities like driving dangerous [1.3.1].
- Gastrointestinal Issues: Diarrhea is another very common side effect, reported in up to 31% of patients in some clinical trials [1.3.2]. Other related issues include nausea, vomiting, and decreased appetite [1.2.1, 1.2.3, 1.2.8]. Changes in appetite and corresponding weight changes (both increases and decreases) are also noted [1.5.4].
- Dry Mouth: Often referred to as "cottonmouth," dry mouth is a frequently cited adverse effect in user surveys [1.5.2].
- Changes in Mood: Some individuals may experience changes in mood, most commonly irritability and agitation [1.2.6, 1.2.8].
Serious Potential Risks and Side Effects
Beyond the more common effects, there are several serious risks associated with CBD use that consumers should be aware of. These often occur at higher doses or with prolonged use and may not have immediately obvious symptoms.
- Liver Injury: A significant safety concern identified by the FDA is the potential for liver injury [1.3.4, 1.6.2]. Evidence from the review of Epidiolex and other studies showed that some users develop elevated liver enzymes, an indicator of liver stress or damage [1.3.3, 1.3.4]. This risk can increase when CBD is taken with other medications that also affect the liver, such as valproate or even common over-the-counter drugs like acetaminophen [1.4.9, 1.3.3]. Symptoms can include nausea, vomiting, upper stomach pain, dark urine, and jaundice (yellowing of the skin or eyes) [1.3.1, 1.3.7].
- Drug Interactions: CBD can affect how other medications work by inhibiting the cytochrome P450 (CYP450) enzyme system in the liver [1.4.2]. This group of enzymes is responsible for metabolizing over 60% of prescribed drugs [1.4.2]. By inhibiting these enzymes, CBD can increase the levels of other drugs in the blood, leading to an increased risk of side effects or toxicity [1.3.3]. This is particularly dangerous for medications with a narrow therapeutic window, such as blood thinners (e.g., warfarin), certain anti-epileptic drugs, and immunosuppressants [1.3.3, 1.4.3].
- Male Reproductive Toxicity: Studies in laboratory animals have indicated potential harm to the male reproductive system, including reduced testicular size, inhibited sperm development, and decreased testosterone levels [1.3.4, 1.6.2]. While these findings are from animal studies, they raise concerns about the potential impact on fertility in human males [1.3.4].
- Mental Health Effects: Although sometimes used for anxiety, CBD can also cause mood or behavior changes like agitation, aggression, panic attacks, or depression. In some cases, it has been associated with suicidal thoughts and tendencies [1.3.1, 1.3.7].
Comparison Table: CBD vs. THC Side Effects
While both are cannabinoids, CBD and THC have different side effect profiles. The most notable difference is THC's psychoactive effect.
| Feature/Side Effect | CBD (Cannabidiol) | THC (Tetrahydrocannabinol) |
|---|---|---|
| Psychoactivity ("High") | Does not cause a "high" [1.2.2] | Causes euphoria and a "high" [1.3.9] |
| Common Side Effects | Drowsiness, diarrhea, reduced appetite, fatigue, irritability [1.2.3] | Altered senses, impaired memory, coordination issues, increased appetite [1.3.9] |
| Anxiety | May cause agitation or anxiety in some cases [1.3.1] | Can cause anxiety, fear, or panic, especially at high doses [1.2.5] |
| Liver Effects | Potential for liver injury, especially at high doses or with other drugs [1.3.4] | Less directly linked, but smoking can damage lungs [1.3.9] |
| Drug Interactions | Significant potential via CYP450 enzyme inhibition [1.4.2] | Also interacts with CYP450 enzymes [1.4.6] |
Unregulated Market and Product Quality
A major issue in the CBD market is the lack of regulation by the FDA for most products [1.3.3]. It is currently illegal to market CBD as a dietary supplement or add it to food [1.6.2]. This regulatory gap means that the product you buy may not have the amount of CBD stated on the label, or it could contain other unknown elements, including THC [1.3.6]. The FDA has issued numerous warning letters to companies making unproven health claims or selling mislabeled products [1.6.3]. For safety, consumers should look for products that have been independently tested by a third-party lab, with results confirmed by a Certificate of Analysis (COA) [1.3.3].
Find out more about the FDA's stance on CBD
Conclusion
While CBD is promoted for a variety of uses, understanding its potential negative side effects is paramount for safe consumption. Common issues like drowsiness and digestive upset are relatively frequent, but more serious concerns such as liver damage, significant drug interactions, and potential reproductive harm cannot be overlooked [1.3.4]. The largely unregulated nature of the market adds another layer of risk due to potential product impurity and inaccurate labeling [1.3.6]. Anyone considering using CBD should first consult with a healthcare provider to discuss potential risks, check for possible drug interactions, and ensure it is a safe option for their individual health circumstances.
