What does CBD do? What cannabidiol can do, what is not proven and its risks

What is CBD?

CBD is short for cannabidiol, a substance in the hemp plant from the group of cannabinoids. Unlike THC, CBD does not cause a high. Germany's Consumer Cannabis Act (Konsumcannabisgesetz, KCanG) therefore explicitly excludes CBD from its definition of cannabis.

CBD comes in three very different forms: as an approved finished medicine, as a preparation made up by a pharmacy (Rezeptur) and as an over-the-counter product from a drugstore or the internet, for example as oil, capsules or gummies. Different rules and different quality standards apply to these forms.

How CBD and THC differ and whether CBD weakens the effect of THC is compared in the article CBD vs THC.

How does CBD work in the body?

CBD works differently from THC. It barely binds to the CB1 receptor, which is responsible for the high. Instead it influences several other targets. Exactly how CBD works in humans is not fully understood.

For the approved CBD medicine, the European prescribing information (summary of product characteristics) describes the mechanism like this: in epilepsy, CBD does not act via cannabinoid receptors. It reduces the overexcitability of nerve cells by influencing calcium balance via the GPR55 receptor and the ion channel TRPV1 and by inhibiting the uptake of the messenger substance adenosine into cells.

The abuse potential of CBD is low. In a study of people who occasionally use drugs, CBD caused hardly any craving or wish to repeat it even in high amounts, clearly less than THC or the sedative alprazolam.

What is CBD approved for as a medicine?

In the EU, one CBD finished medicine is approved as an oral solution. According to the prescribing information, it is used as an add-on treatment for seizures in Lennox-Gastaut syndrome or Dravet syndrome, there in combination with the active ingredient clobazam, and for seizures associated with tuberous sclerosis complex, in each case in patients aged 2 years and older.

These are rare, severe forms of epilepsy that usually begin in childhood. Treatment should be started and supervised by doctors experienced in treating epilepsy, with regular checks of liver values.

In addition, CBD can be made up by a pharmacy as a preparation, for example as an oily CBD solution following a recipe in the German New Formulary for Pharmacy Preparations (Neues Rezeptur-Formularium, NRF). CBD in medicines is prescription-only but not a narcotic.

What is known about the effects of CBD on other conditions?

For most uses for which CBD products are advertised, robust evidence is lacking. This applies, for example, to anxiety, sleep problems, stress, pain or inflammation. There are laboratory experiments, animal studies and small studies in humans, but hardly any large, well-designed studies with a clear result.

A systematic review in the journal Lancet Psychiatry analysed all available studies on cannabinoids for mental disorders in 2019, including depression, anxiety disorders, ADHD, post-traumatic stress disorder and psychoses. Result: there is little evidence of improvement, and only a few randomised studies of pure CBD were available.

This does not mean that CBD is definitely ineffective. But it does mean: if you take CBD with a specific expectation, you are not currently relying on established findings. Persistent symptoms should be assessed by a doctor.

What are the side effects of CBD?

CBD is not free of side effects. The best data comes from the approval studies of the CBD medicine. There, the most common side effects were sleepiness (23 per cent), reduced appetite (21 per cent), diarrhoea (20 per cent), fever (16 per cent), vomiting (12 per cent) and tiredness (10 per cent).

The liver is particularly important. CBD can raise liver values (transaminases) depending on the amount, especially together with the epilepsy medicine valproate. That is why liver values are checked before treatment starts and regularly afterwards. CBD must not be used if values are greatly raised.

Further notes in the prescribing information: CBD can lead to weight loss, trigger irritability or aggression and increase sleepiness, especially with alcohol or other sedating substances. As with other epilepsy medicines, patients should be monitored for signs of suicidal thoughts.

These figures come from studies with comparatively high amounts in seriously ill children and adults. They cannot be transferred one to one to CBD oils from shops. But they show that CBD is a pharmacologically active substance.

• Very common: sleepiness, reduced appetite, diarrhoea, vomiting, fever, tiredness
• Common: nausea, raised liver values, irritability, lethargy, skin rash, weight loss
• Important: have liver values checked, do not combine with alcohol, do not drive while you feel sleepy

Which drug interactions does CBD have?

CBD has many interactions because it is broken down in the liver by the same enzymes as numerous medicines and inhibits some of them. According to the prescribing information, this affects the enzymes CYP2C19, CYP3A4, CYP1A2, CYP2C8 and CYP2C9, among others.

One example: together with the epilepsy medicine clobazam, the level of its active breakdown product rises three- to fourfold. With everolimus, a medicine used among other things after organ transplants, the amount in the blood rose to about 2.5 times. Conversely, substances such as rifampicin, carbamazepine or St John's wort lower the CBD level.

The Senate Commission on Food Safety of the German Research Foundation (DFG) points out that interactions are possible even at amounts found in dietary supplements. If you take medicines regularly, you should therefore only take CBD after talking to your doctor. An overview of critical combinations is given in the article Cannabis drug interactions.

CBD oil: effects and absorption in the body

CBD oil is usually dropped under the tongue or swallowed. How much CBD reaches the blood is surprisingly poorly studied in humans. A systematic review from 2018 found only 24 studies with data on the absorption of CBD. None of them determined the absolute bioavailability after swallowing.

What is known: fat in food greatly increases absorption. In a study of healthy people, the peak CBD concentration in the blood rose fivefold after a high-fat meal and the total amount fourfold. It also rose with milk or alcohol. With regular use, a half-life of two to five days was described.

For everyday effects, this means: the same amount of CBD oil can arrive very differently depending on the meal.

How good are CBD products from shops?

The quality of over-the-counter CBD products varies widely. In an analysis of 84 CBD products bought online, published in the journal JAMA, only 31 per cent contained roughly as much CBD as stated on the label. The rest contained clearly more or clearly less. THC was also found in 18 of the 84 products.

For you this means: the amount on the label is not a reliable value, and traces of THC are possible. This can lead to a positive result in drug tests at work or on the road. What this can mean for your driving licence is explained in the guide Driving with a cannabis prescription.

A distinction is often made between full-spectrum products with other plant substances and isolates with pure CBD. Full-spectrum products can also contain THC. How long THC can be detected is explained in How long does THC stay in your system?

How much CBD is considered safe?

In February 2026, the European Food Safety Authority (EFSA) set a provisional safe level for CBD as a food: 0.0275 milligrams per kilogram of body weight per day. For an adult weighing 70 kilograms, that is around 2 milligrams per day. Many products contain several times this amount per serving.

For three groups EFSA could not set any safe amount at all: people under 25, pregnant and breastfeeding women, and people who take medicines. Open questions mainly concern the liver, the hormonal system, the nervous system and reproduction.

This value is not a recommendation for use but a cautious upper limit for foods. The amounts used in drug therapy are much higher and are supervised by a doctor there.

Is CBD legal in Germany?

CBD as a substance is not a narcotic in Germany and does not fall under the Consumer Cannabis Act. But that does not mean every CBD product may be sold legally. What matters is what a product is marketed as.

Foods and dietary supplements containing CBD count as novel foods because no significant consumption before 15 May 1997 has been documented. There is no authorisation so far. The Federal Office of Consumer Protection and Food Safety (BVL) therefore classifies such products as not marketable. Health claims are not permitted for CBD foods.

CBD in medicines is prescription-only. Smokable CBD flowers are parts of the hemp plant: they only fall outside the KCanG if they meet the requirements for industrial hemp (Nutzhanf), including a maximum of 0.3 per cent THC and a purpose that rules out misuse for intoxication. The legal situation around THC in Germany is explained in Is cannabis legal in Germany?

CBD and THC in cannabis treatment

Medical cannabis flowers and extracts are classified by their THC and CBD content: THC-dominant, balanced or CBD-dominant. Which profile is an option is decided by the doctor based on symptoms, previous experience and risks.

A common assumption is that CBD buffers the unwanted effects of THC. However, a randomised double-blind study with 46 participants found no weakening of the acute effects of THC on memory and psychotic symptoms at common mixing ratios. A CBD share is therefore no licence for a lot of THC. An overview of medical cannabis in Germany is given in the guide Medical cannabis in Germany.

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