CBD and schizophrenia: current research

To mark World Schizophrenia Day, we review the current research on CBD in this illness. The first thing you should know is that CBD is not currently an approved medicine for schizophrenia and that, for the time being, its use is not indicated.

CBD, or cannabidiol, is a non-psychoactive compound found in cannabis plants. In recent years, this compound has been put forward as a possible treatment for schizophrenia. However, it is important to stress that the use of CBD for schizophrenia is currently still at the research stage, so its use is contraindicated. In this post we review the research on the subject.

What is schizophrenia?

Schizophrenia is a serious mental illness that affects how a person thinks, feels and behaves. Symptoms can include hallucinations, delusions, disorganised speech, erratic behaviour and social withdrawal. It is a chronic illness and usually requires long-term treatment.

How is schizophrenia treated?

Treatment may include antipsychotic medication and therapy. Schizophrenia is the most common illness within the group of “psychoses”, a term used in psychiatry for illnesses in which there is a loss of contact with reality.

What is the link between cannabis and schizophrenia?

Schizophrenia does not have a single cause; it is explained by a combination of genetic and environmental factors. There is a statistical association between some patterns of cannabis use and the later development of schizophrenia (1), which does not mean that cannabis use is either a necessary or a sufficient cause.

It is also known that, in people diagnosed with schizophrenia, cannabis use increases the symptoms of the illness and the number of hospital admissions, and worsens the prognosis.

Is medical cannabis an option for schizophrenia?

Advances in knowledge about cannabinoids have made it possible to establish that the component of cannabis that exacerbates or worsens schizophrenia is tetrahydrocannabinol (THC), the same compound responsible for the psychotropic and psychoactive effects of cannabis. High doses of THC can produce psychotic symptoms (such as those seen in schizophrenia) in susceptible people.

In 1982 it was shown in humans, for the first time, that cannabidiol (CBD) could reverse these effects produced by THC (2). Therefore, at present, research on medical cannabis in relation to schizophrenia focuses exclusively on cannabidiol.

Are there studies suggesting that CBD may be useful in schizophrenia?

CBD has been tested in several of the animal models routinely used to evaluate antipsychotic drugs at the preclinical stage. There are studies in genetically modified mice used for this purpose in which it is suggested that administering CBD has antipsychotic properties (3). In animal models, cannabidiol has also been shown to enhance anandamide signalling in the brain, a process linked to the development of schizophrenia (4). In short, taken together, the animal research data suggest that CBD may be a good antipsychotic (5).

Are there cases in humans in which the effect of cannabidiol on schizophrenia has been tested?

Anecdotal reports of patients with schizophrenia who have improved significantly using CBD as part of their medical treatment have been recorded since at least 1995 (6, 7, 8). These cases have been published in prestigious scientific journals accepted by the medical community. But case reports can never be considered proof of a drug’s efficacy. They are an indicator used to move on to the next stage: clinical trials.

Clinical trials on the efficacy of CBD in patients with schizophrenia

The results of the only two good-quality clinical trials available on cannabidiol and schizophrenia were published in 2018. A study of 88 patients in the UK found improvement when CBD was added to the patients’ usual treatment for 6 weeks (9). Another US study with a similar design, involving 36 patients, found no beneficial effect (10).

What doses of CBD have been used in clinical trials on cannabidiol and schizophrenia?

In the human clinical trials we have just mentioned, the dose used by the British team was 1,000 mg of CBD a day, taken orally, and the one used by the US team was 600 mg of cannabidiol a day. The difference in results can probably be explained, at least in part, by the different dosage.

Are there more clinical trials currently under way?

Yes. There are clinical trials under way on the use of CBD for schizophrenia, with large numbers of patients, at institutions as prestigious as the Central Institute of Mental Health in Mannheim (Germany) (11), the University of Copenhagen (12), the University of California’s Center for Medicinal Cannabis Research (13) and King’s College London (14).

Most of these clinical trials are recruiting patients or already under way, and the results are expected to be available between 2023 and 2024. These studies use doses of 1,000 mg of CBD a day, although some of the trials exploring specific aspects use doses of 300–400 mg of CBD a day.

How does CBD work for schizophrenia?

The antipsychotics available on the market are very effective drugs for some symptoms of schizophrenia, such as delusions and hallucinations. But their main drawback is their side effects: sedation, drowsiness, difficulty concentrating, obesity and diabetes, muscle problems, sexual problems…

Many patients with schizophrenia can lead a reasonably normal life while taking their prescribed medication. But side effects are the most common reason for stopping medication, so having antipsychotics with fewer side effects is a priority. CBD’s few side effects make its potential use as an antipsychotic particularly interesting.

CBD and schizophrenia medication

Could CBD replace other antipsychotic drugs?

It is very important to stress that in all the clinical trials available to date, CBD has been added to conventional medication. In other words, these are studies comparing the effect of adding CBD or a placebo to the treatment a patient is already taking.

The antipsychotic effect of CBD would, on a doctor’s prescription, make it possible to reduce the dose of the conventional antipsychotic, lowering the frequency and severity of side effects which, as we have already pointed out, are the main problem with the drugs available.

There are no data suggesting that CBD can be used as an antipsychotic on its own. In this regard, replacing an antipsychotic drug with cannabidiol in a patient with schizophrenia is absolutely contraindicated.

Are there interactions between CBD and antipsychotic drugs?

There are theoretical and laboratory data indicating that CBD could alter the blood concentrations of the two most commonly used antipsychotics: risperidone and olanzapine (15). However, there are no data indicating that these preliminary findings have any impact in humans. In fact, as we have pointed out, all the clinical trials carried out have added cannabidiol to usual medication without any problems of this kind being reported.

Are there other lines of research on CBD and psychotic disorders?

We pointed out earlier that, in general, cannabis use worsens the condition of people diagnosed with schizophrenia. Despite this, some patients continue to use cannabis compulsively and in a disordered way. The co-occurrence of two disorders (schizophrenia + cannabis use disorder) is known as “dual diagnosis”, and CBD is an interesting treatment option that is already being put into practice (16), although its effectiveness has not yet been proven and it is therefore not advisable.

In summary, CBD, or cannabidiol, is emerging as a possible therapeutic option for schizophrenia, but more research is needed before this can be stated with certainty.

Ultimately, it is absolutely essential that patients with schizophrenia seek advice from their specialist doctor before using CBD and other cannabis-derived products.

This post is for information purposes only and its content is not intended to prevent, diagnose or treat any disease or symptom. Its content may complement, but never replace, professional diagnosis or treatment. CBD is not an approved medicine for schizophrenia. Cannactiva products are not medicines. Talk to your doctor if you have any questions about schizophrenia and before using CBD.