Side effects and safety of medicinal cannabis

Updated 03 August 2023

The products included in the medicinal cannabis pilot programme have not been studied in the same systematic way as authorised medicines. This means that the scientific evidence of side effects is very limited.

The Danish Medicines Agency monitors side effects (or adverse reactions) and the safety of medicinal cannabis.

It is very important that doctors and patients report all suspected adverse reactions of medicinal cannabis to the Danish Medicines Agency so we can learn more about how the different products affect the body.

We collect adverse reaction reports (ADR reports) to identify any signals of new or changed risks about the pilot programme’s cannabis end-products. These reports form part of the basis of our ongoing assessment of the safety profiles of the products.

We subject the ADR data to scientific evaluation, consider options for risk minimisation and risk prevention, and, if needed, we take appropriate measures in relation to the distribution and dispensing of the products.

What we know about side effects of THC and CBD

The knowledge that the Danish Medicines Agency currently has about side effects (or adverse reactions) of medicinal cannabis is primarily based on international clinical studies of cannabis-based medicines such as Sativex, Cesamet/Nabilone and Marinol.

Some of the side effects of THC-containing products are: sleepiness, dizziness, mood changes, anxiety, concentration and memory problems, low blood pressure causing fainting, and effects on the ability to drive. Among the more serious psychiatric symptoms are: depression, hallucinations, paranoia, delusions and suicidal thoughts. If you use THC-containing products for longer periods, you are at risk of developing dependence. This has been seen when patients with chronic pain are treated with medicinal cannabis. In general, there is limited evidence of adverse reactions with long term use, but negative effects on concentration and learning ability cannot be ruled out.

There is only very limited knowledge about the adverse reactions caused by CBD. There is evidence that CBD may affect the liver and possibly also the immune system.

You can find more information about warnings and adverse reactions related to medicinal cannabis in the guideline for doctors.

Report all side effects of medicinal cannabis

Doctors in Denmark are required to report all suspected adverse reactions of cannabis products included in the pilot programme to the Danish Medicines Agency. Patients and relatives (general public) can also report suspected adverse reactions to the Danish Medicines Agency.

We would like to encourage all patients who experience side effects (adverse reactions) from medicinal cannabis to tell their doctor and to report the side effects to the Danish Medicines Agency. You do not have to be sure that the medicinal cannabis you are taking is causing the symptoms. Only a suspicion is needed for you to report the symptoms as side effects.

To submit a report, please go to the page:

Report a suspected side effect of cannabis end-products – for patients and relatives.

We collect side effect reports (ADR reports) to find out if there are signals of new or changed risks in relation to the cannabis products of the pilot programme. The ADR reports are part of the basis of our ongoing assessment of the safety of the products.

You can read the ADR overviews for the individual cannabis products below. But before you do, it is important that you review the terms of use of the interactive ADR overviews.

Doctors have a duty to report suspected adverse reactions

Doctors are required to report all suspected adverse reactions of cannabis end-products to the Danish Medicines Agency. Serious adverse reactions must be reported to us no later than 15 days after the doctor became aware of an occurrence.

Other healthcare professionals, patients and relatives have the option of reporting suspected adverse reactions

Other health professionals, patients and relatives have the option of reporting suspected adverse reactions of cannabis end-products to the Danish Medicines Agency.

To submit a report, please go to the page:

Report a suspected adverse reaction of cannabis end-products – for healthcare professionals.

ADR overviews

The Danish Medicines Agency receives and registers reports of suspected adverse drug reactions (suspected side effects) of cannabis end-products covered by the Act on a Medicinal Cannabis Pilot Programme. In the adverse drug reaction (ADR) overviews, we publish data from these reports.

While the ADR overviews can be a useful tool to identify possible safety problems, they do not offer a complete overview of the risks that might be associated with the use of cannabis end-products. Therefore, conclusions on the safety and risks of the products cannot be made on the data shown in the ADR overviews alone.

ADR overviews cannot be used to calculate the probability of experiencing adverse reactions from a cannabis end-product, and you cannot compare the safety of different products by comparing the figures in the ADR overviews.

When doctors, healthcare professionals, patients and relatives report adverse reactions to the Danish Medicines Agency, a suspicion that symptoms are adverse reactions of a product is enough to file a report. A reported suspected adverse reaction is therefore not the same as a documented, actual link between the product and the experienced adverse reaction.