CBD side effects: what you should know before using it

Cannabidiol, known simply as CBD, has gone from a niche ingredient to a visible presence in pharmacies, herbalists and specialist shops all over Spain. Its popularity is growing alongside the studies exploring its possible uses, from managing stress to supporting a good night’s sleep. However, as with any active compound, CBD is not free from unwanted effects. Knowing about them before you start is the smartest way to get the most out of it without any surprises.

What CBD is and what it is used for

CBD is one of more than a hundred cannabinoids found in the Cannabis sativa plant. Unlike THC, the psychoactive cannabinoid responsible for the “high”, CBD does not alter your state of mind or cause dependence, according to the World Health Organization. This makes it a compound of interest both for biomedical research and for people looking for natural wellbeing.

Some preliminary research suggests that CBD may act on the body’s endocannabinoid system, a network of receptors involved in functions such as pain response, inflammation, mood and the sleep cycle. Based on this data, many people add it to their routine to:

• Encourage relaxation and ease the feeling of everyday tension.
• Support more restful sleep.
• Complement the management of mild muscle or joint discomfort.
• Accompany medical treatment under professional supervision.

At Maionais you will find products such as CBD oils (from €29) and CBD buds in different strains, all made from industrial hemp with less than 0.2% THC, in line with European regulations. If you want to check the exact composition before buying, you can view our lab certificates, where we publish third-party analyses for every batch.

The most common side effects of CBD

The scientific community considers CBD to have a favourable safety profile, but that does not mean it has no adverse effects. Most are mild and temporary, and tend to appear when people take higher doses than they need or when the body is not yet used to the molecule.

Drowsiness and fatigue

One of the most frequently reported side effects is a feeling of tiredness or sleepiness, especially at high doses. Paradoxically, some preliminary studies point to a more stimulating effect at low doses. If you are taking it for the first time, avoid driving or operating machinery until you know how it affects you.

Dry mouth

CBD interacts with receptors in the salivary glands, which can temporarily reduce saliva production. The solution is simple: stay well hydrated throughout the day.

Changes in appetite and weight

Some people experience an increased appetite; others report a certain loss of interest in food. This effect varies considerably from person to person and tends to settle with continued use.

Liver changes at high doses

Animal studies and some human data (mainly linked to the drug Epidiolex, which contains CBD at very high therapeutic doses) have shown that CBD can raise liver enzymes. With normal use at low or moderate doses this risk is low, but it is worth keeping an eye on if you have a pre-existing liver condition or use other substances that affect the liver.

CBD interactions with medication

This is probably the most important aspect from a safety point of view. CBD is metabolised mainly in the liver through the cytochrome P450 enzyme system, specifically the CYP3A4 and CYP2C19 isoenzymes. These same enzymes are responsible for breaking down a large number of common medicines. When CBD competes with them for the same metabolic pathway, the following can happen:

• The concentration of the medicine in the blood increases, raising the risk of toxic effects.
• The medicine is cleared faster than expected, reducing its effectiveness.

Some drugs with known or likely interactions include:

Anticoagulants (warfarin)

Several studies suggest that CBD may inhibit the metabolism of warfarin, which would raise its blood levels and the risk of bleeding. If you take anticoagulants, talking to your doctor first is essential.

Anti-epileptic drugs

CBD has been studied in combination with drugs such as clobazam and valproate. Some studies indicate that it may enhance both their therapeutic effects and their side effects. In these cases, monitoring should always be carried out under the supervision of a neurologist.

Immunosuppressants

Ciclosporin and tacrolimus, used in transplants and autoimmune diseases, are also metabolised through the pathways affected by CBD, which could alter their plasma levels.

Other drugs with a narrow therapeutic window

Antidepressants, anti-anxiety medication, antipsychotics, antiarrhythmics and certain antibiotics may be affected. If you take any medication regularly, always check with your doctor or pharmacist whether CBD is compatible with it.

Who should avoid CBD or seek advice first

Although CBD is well tolerated by most healthy adults, there are groups of people for whom caution is the rule, not an option:

Pregnant and breastfeeding women

Scientific evidence on the safety of CBD during pregnancy and breastfeeding is still very limited. The general recommendation from health authorities is to avoid it during these periods until more data is available.

Minors

Except under strict medical indication (as in certain types of drug-resistant epilepsy), CBD is not recommended for children and teenagers.

People with liver disease

Since CBD is processed in the liver and can raise liver enzymes at high doses, anyone with hepatitis, cirrhosis or other liver conditions should seek advice before adding it to their routine.

People taking multiple medications

The more medicines taken at the same time, the greater the risk of interactions. In these cases, supervision by a healthcare professional is not just advice but a necessity.

People with low blood pressure

Some preliminary research suggests that CBD could cause a slight drop in blood pressure, which may be relevant for people who already have low blood pressure or take antihypertensive medication.

How to minimise the risks

Using CBD responsibly is not complicated, but it does mean following a few basic guidelines that make the difference between a positive experience and a frustrating one:

Start with the lowest possible dose

The “start low and go slow” principle is the advice specialists repeat most often. A starting dose of 5–10 mg of CBD per day lets you observe how your body responds before increasing it. Your body needs time to adapt.

Choose products of verified quality

Not every product on the market contains what it claims to contain. Always look for brands that publish independent lab analyses. At Maionais, all our products come with third-party analytical certificates available on our website, where you can check the actual CBD concentration, the absence of pesticides and the THC levels.

Pay attention to the method of use

Topical use (creams, balms) significantly reduces systemic exposure and therefore the risk of adverse effects or interactions. Sublingual oil offers more predictable absorption than oral capsules. Inhaled CBD buds and CBD resins act quickly, but inhalation has its own respiratory considerations that are worth weighing up.

Tell your doctor

It may seem like obvious advice, but many CBD users do not mention it during their medical appointments. CBD is an active compound and deserves the same level of transparency as any supplement or medicine.

Take regular breaks

Taking periodic breaks from use can help prevent tolerance and lets you reassess whether the benefits are still noticeable. There is no single protocol: listen to your body and adjust accordingly.

Frequently asked questions

Is CBD addictive or habit-forming?

The WHO has concluded that CBD shows no potential for abuse and does not cause dependence in humans. Unlike THC, it does not significantly activate the brain’s reward circuits. You can stop using it without expecting withdrawal symptoms.

Can CBD cause a positive drug test?

Standard drug tests detect THC, not CBD. However, some low-quality products may contain traces of THC above the declared amount. Buying products with an analytical certificate confirming a THC level below 0.2%, such as those from Maionais, keeps this risk to an absolute minimum.

How long do side effects take to appear?

The most common adverse effects, such as drowsiness or digestive discomfort, usually appear within the first few hours after taking it. Liver changes associated with very high doses appear later and require regular blood tests to detect.

Is it safe to take CBD and alcohol together?

Combining CBD with alcohol or other central nervous system depressants can increase sedation and drowsiness. Although there is no evidence that this combination is dangerous at low doses in healthy adults, the sensible thing is to avoid it, especially if you are going to drive or need to stay alert.

Is CBD legal in Spain?

CBD derived from industrial hemp with less than 0.2% THC is legal in Spain for external use and aromatherapy. Selling it as a food supplement is subject to restrictions from AESAN (the Spanish Agency for Food Safety and Nutrition). At Maionais all our products comply with current regulations and you can buy them without any problem. If you have doubts about the legality of a specific format, we recommend consulting a legal specialist or our team.

Scientific sources and references

• WHO Expert Committee on Drug Dependence (2018). Cannabidiol (CBD) Critical Review Report. World Health Organization, Geneva.
• Iffland, K. & Grotenhermen, F. (2017). “An Update on Safety and Side Effects of Cannabidiol: A Review of Clinical Data and Relevant Animal Studies.” Cannabis and Cannabinoid Research, 2(1), 139–154.
• Devinsky, O. et al. (2018). “Effect of Cannabidiol on Drop Seizures in the Lennox–Gastaut Syndrome.” New England Journal of Medicine, 378, 1888–1897.
• Millar, S.A. et al. (2019). “A Systematic Review on the Pharmacokinetics of Cannabidiol in Humans.” Frontiers in Pharmacology, 10, 1365.