Potential side effects

THC and CBD, currently the most common types of medical cannabis treatment, do have a limited profile of short and long term side effects.

Short term side effects

CBD can cause mild drowsiness, dry mouth and lightheadedness. Some patients may experience a mild drop in blood pressure, including mild hypertension, so slow movements can be advisable after administration.

There is some evidence that mild gastrointestinal upset can occur, although it’s thought this relates more to the carrier oil used to make CBD digestively soluble.

Overall, though, CBD is safe with very few side effects. The estimated three percent of users with a marked sensitivity may initially be recommended lower doses.

As the main psychoactive component of cannabis, THC can produce more notable side effects. Disorientation, dizziness or general confusion can be observed, as can be a sense of euphoria.

In more severe cases, anxiety, paranoia or hallucinations can occur and there is some evidence that psychosis can be triggered in those predisposed to psychological conditions. Depression is a potential outcome of cannabis use, although adversely cannabis is also investigated for treating depression.

Many patients will experience an observable increase in heart rate, which can be problematic if at increased risk of heart attack or strokes.

Long term side effects

While CBD use is not generally associated with adverse side effects, THC is known to potentially cause a range of issues, notably if mismanaged or abused. The primary concerns of sustained THC use are in its psychotic properties, and the potential to develop dependency on the substance.

Cannabis dependency is thought to exist in around 10% of users (as compared to 15% for cocaine use and 30% for tobacco use), and if sustainably abused can result in reduced cognitive ability. It is known that cannabis use in young populations can have longer lasting adverse psychological and cognitive effects and should be very carefully managed where clinically applied.

Adversely, however, CBD is thought to attenuate the psychoactive effect of THC, so there is potential for safe THC administration if properly balanced.

Other long term concerns with cannabis use relate to the carcinogenic effects of smoking substances, particularly with regard to the common habit of mixing cannabis with tobacco. Clinically, though, smoking is strongly advised against.

In very rare cases, a severe reaction to cannabis use known as cannabis hyperemesis syndrome has been observed, This is characterised by cyclical periods of vomiting and often stomach pain, and can last for several days. It is usually self-limiting and tends to occur in regular heavy recreational cannabis use and so we can’t absolutely be certain that the cause is purely cannabis related. It is very rare in the context of medical cannabis usage. Sometimes it can be very severe and hospital admission is required particularly for rehydration, usually though it stops once the cannabis usage is stopped.


There is a limited set of conditions that exclude the use of cannabis. These are:

  • Allergy to cannabis
  • Predisposition to psychosis or personality disorder
  • Pregnancy

Additionally there are certain drug interactions that would require caution around the administration of cannabis medicines. This primarily applies to how other drugs affect the metabolization of cannabis compounds, meaning that cannabinoids can either be retained in the body for longer than desired, or broken down too quickly to allow for therapeutic benefit.

Are you experiencing any side effects?

Adverse events should be reported. Reporting forms and information can be found at www.yellowcard.mhra.gov.uk/

We are regulated by GPHC

Registered address:

Eprescriptions Ltd t/a Dispensary Green

Unit 3, Sherwood Energy Village, Newton Hill, New Ollerton
NG22 9FD

Superintendent pharmacist:

Mehraan Sattar

GPHC Number: 2211738