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Cannabis and the brain: how harmful is it really?

Medical cannabis has been legalized in several countries around the world. It can contain more than 100 ingredients that can have both positive and negative effects. The two most important representatives are tetrahydrocannabinol (THC), the psychotropic ingredient of cannabis, and cannabidiol (CBD), which is non-psychotropic and partially counteracts the properties of THC (1).

In recent years, cannabis has been increasingly used medicinally. It can be used for completely different diseases. Through medically prescribed cannabis, the therapeutic effect of cannabis can be used specifically and the side effects can be controlled.

Recreational use is to be distinguished from this. Cannabis can be legally purchased in several countries not only as medicine but also for recreational use. Against this background, it is even more important to address how cannabis can affect the brain. There are publications that clearly show that chronic use of cannabis could be harmful to the brain. This is especially true for recreational use in younger or very young people. Let’s take a closer look at the research on the long-term effects of cannabis on the brain.

How does cannabis affect the human brain?

Because of its history as an illegal narcotic, most studies on the effects of cannabis on the brain have been conducted on subjects with chronic recreational cannabis use. In these individuals, cannabis has been shown to cause structural changes in brain anatomy. This particularly affects the hippocampal area. This is due to the high density of cannabinoid receptors in the hippocampal region.(2)

In addition, neuroscience research has shown that although heavy chronic use of cannabis can lead to changes in brain function, these changes are not associated with noticeable performance problems. This suggests that performance is maintained by brain regions not normally involved in specific cognitive function.(2)

Regarding the effects of cannabis on cognitive abilities, these are most striking in adolescent chronic users. While results on intelligence are conflicting, many studies confirm the negative effects on memory and information processing, among others. Of note and concern is that these effects worsen with increasing amount, frequency, and duration of cannabis use in adolescence.(2)

Despite these findings, it is important to point out that there are many inconsistencies when it comes to neurological imaging studies on the effects of cannabis. There is often wide variation in the measurement of quantity, frequency, and duration of cannabis use. In addition, the lack of consistent study design and methods can lead to conflicting results.(2)

How medical cannabis can be used safely

As with any drug, the context in which it is used determines its efficacy. When used medicinally, cannabis can have positive therapeutic effects with manageable side effects. To ensure this, patients must not only follow the prescribing physician’s instructions, but also report changes and side effects accordingly.

Effective risk management can detect and prevent problems associated with potential cannabis side effects. The following recommendations for physicians can help ensure patient safety (5):

1. Ensuring a secure supply
It is imperative that patients have access to a reliable pharmaceutical-grade medical cannabis product to ensure consistent dosing.

2. Screening of patients
Factors that might make a person more susceptible to developing dependence even when using medical cannabis (e.g., young age, chronic cannabis use in the family, mental illness, current heavy use of cannabis) are important to consider when prescribing.

3. Regular monitoring of the amount taken
Targeted and regular monitoring of medical cannabis use is necessary to minimize the risk for side effects and the development of dependence.

4. Personalized treatment
Treatment with medical cannabis should be personalized. The following aspects can be adjusted depending on the disease state and individual disease process:

  • THC to CBD ratio
  • Frequency of use
  • Mode of administration

Genetic differences in cannabis receptors or metabolism between different patients may also contribute to treatment success.
From this, a different approach can be established from patient to patient and the sometimes completely different risk for the development of a dependency can be addressed.

5. Balancing patient need with health risk.
The risks of medical cannabis must be weighed against other established medications, some of which may themselves have a higher potential for side effects. When prescribing, the physician and patient must weigh this trade-off together, especially if use is likely to be required in the long term.


All in all, the risks of cannabis for the brain are by no means negligible.

Some studies show that heavy chronic recreational use of cannabis can have detrimental effects on brain development, which is especially true when used at a young age. While the data on the effects on adolescents are very clear, further consistent and reliable studies are needed to determine the effects of cannabis on the adult brain.

Nevertheless, cannabinoids have positive therapeutic effects when used responsibly. Therefore, medical cannabis is also subject to prescription. Physicians must consider both the positive and negative properties of cannabis when prescribing it to treat a disease. This ensures that patients receive maximum therapeutic benefit with minimal side effects.


Müller-Vahl KR, Grotenhermen F. Cannabis und Cannabinoide: in der Medizin. 1st ed.
Berlin: MWV Medizinisch Wissenschaftliche Verlagsgesellschaft; 2019. 359 p.

Burggren AC, Shirazi A, Ginder N, London ED. Cannabis effects on brain structure, function, and cognition: considerations for medical uses of cannabis and its derivatives.
Am J Drug Alcohol Abuse. 2019;45(6):563–79.

Rubino T, Parolaro D. The Impact of Exposure to Cannabinoids in Adolescence: Insights From Animal Models. Biol Psychiatry. 2016 Apr 1;79(7):578–85.

Albaugh MD, Ottino-Gonzalez J, Sidwell A, Lepage C, Juliano A, Owens MM, et al. Association of Cannabis Use During Adolescence With Neurodevelopment. JAMA Psychiatry. 2021 Sep 1;78(9):1031–40.

Schlag AK, Hindocha C, Zafar R, Nutt DJ, Curran HV. Cannabis based medicines and cannabis dependence: A critical review of issues and evidence. J Psychopharmacol Oxf Engl. 2021 Jul;35(7):773–85.

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So kaufen Sie medizinisches Cannabis in Deutschland?
Seit dem Inkrafttreten des „Cannabis als Medizin” Gesetzes am 10. März 2017 ist die Verschreibung von Cannabis in Deutschland zu therapeutischen Zwecken legal. Unter ärztlicher Anleitung können Patienten ein Rezept für medizinisches Cannabis erhalten und damit medizinisches Cannabis in verschiedenen Formen erhalten und anwenden.