BlogWhat are the most common side effects of medical cannabis?

What are the most common side effects of medical cannabis?

7 min read

Sam North

What are the most common side effects of medical cannabis

The first question that most new patients have (often before even reaching out to a medical cannabis clinic) is -

"What are the most common side effects encountered with medical cannabis?"

While cannabis-based treatment options have been shown to offer patients a very favourable safety profile with a wide range of therapeutic benefits - like almost all medical options, there are side effects to consider.


Some common medical cannabis side effects include slight dizziness, a dry mouth, changes in how hungry they feel, a shift in mood, raised blood pressure, racing heartbeat, and higher anxiety levels.

While a few of these side effects do sound concerning, they are most often on the milder side and generally subside quickly.

If you experience any unwanted side effects from medical cannabis options, keep in mind that they can usually be managed and minimised through fine-tuning your dosage and proper strain or product selection.

There is a bit more to this, so let's dive right in.

The side effects of THC and CBD explained

Both THC and CBD are classed as cannabinoids, and both offer patients a natural treatment solution. However, they do differ in some specific ways, with side effects being one of them.

What are the side effects of medical cannabis containing THC?

Products containing more than 0.2% THC (or 1 mg per container) are only legally available in the UK if a specialist doctor prescribes them.

THC is the major psychoactive component produced by Cannabis sativa L. plants, and while it has been shown through rigorous research to be an effective and safe therapeutic option for the overwhelming majority of patients, it does come with some side effects to be aware of.

The more common side effects of medical cannabis containing THC include:

  • Lightheadedness
  • Dry mouth
  • Increased appetite
  • Changes in mood (e.g. feeling more relaxed or socially withdrawn)
  • Red eyes
  • Racing heart beat or increased heart rate
  • Changes in blood pressure (usually a slight increase)

High doses of THC can also induce feelings of anxiety, paranoia, or panic in some people - but, when prescribed through a specialist and the dosage is monitored, these side effects can generally be avoided.

What are the side effects of medical cannabis containing CBD?

Medical cannabis products with higher levels of CBD and low or no THC content have also shown to be very safe and come with slightly less risk than those with high THC percentages. 

CBD products are allowed to be sold OTC in the UK, as long as each container has no more than 1 mg of THC.

The more common side effects of medical cannabis containing CBD include:

  • Dry mouth
  • Feeling light-headed
  • Changes in appetite (often decreased)
  • Gastrointestinal upset
  • Fatigue or drowsiness

Some patients may also experience changes in their mood, but these are generally milder than those experienced with THC administration.

Do medical cannabis oil side effects differ from other forms of medical cannabis?

They can - it depends on the route of administration.

In the UK, medical cannabis options are available in multiple forms, including oils, capsules, sprays, and dried flower.

Medical cannabis oils are usually prescribed for sublingual (under the tongue) administration, but may also be taken orally.

The National Institute for Health and Care Excellence (NICE) considers both routes to be effective and safe therapeutic options. However, both sublingual and oral administration can lead to the oil reaching the digestive tract, which can cause unwanted side effects such as nausea or gastrointestinal discomfort for some patients.

Can the side effects of medical cannabis be effectively managed?

In the vast majority of cases, yes, medical cannabis side effects can be effectively managed and sometimes totally mitigated.

Cannabis-based therapy is a very individual process, and the side effects that patients experience can be greatly impacted by things like their unique body composition, the specific treatment option being used, and how long they have been using it.

There is often a short 'trial-and-error' period when patients first start with cannabis-based treatment options. Everyone responds differently, so finding the right dosage and administration method can take a little time.

Will titrating medical cannabis products reduce the risk of side effects?

The short answer is yes - in fact, titration is the most common approach by medical professionals when prescribing cannabis-based therapies.

Titration is a process of gradually increasing the dosage size until the 'sweet-spot' is found. This allows your body to slowly get used to the treatment, which helps minimise the risk of any unwanted medical cannabis side effects popping up.

High doses of THC can also induce feelings of anxiety, paranoia, or panic in some individuals, but when prescribed through a specialist and the dosage is monitored, these side effects can generally be avoided.

Medical cannabis side effects FAQs

What are the side effects of prolonged cannabis use?

While medical cannabis offers a natural, generally safe therapeutic solution, there can be some issues with heavy, prolonged, unsupervised use. This is why it's essential to always follow the advice and guidance of your prescribing specialist, and to report back to them any sudden changes or reactions.

The potential side effects of prolonged, unsupervised cannabis use can include memory issues, mood changes, changes in appetite, and cognitive impairment.

Again, always follow the guidance of your doctor and never self-medicate.

What are some uncommon side effects of medical cannabis?

While exceedingly rare, there can be a few severe reactions to medical cannabis. Some of these can include:

  • Hallucinations
  • Panic attacks
  • Allergic reactions

Anyone with a history of psychosis or severe mental health issues should speak to their current clinical team before reaching out to a medical cannabis specialist. The specialist you choose to reach out to should have experience prescribing medical cannabis options to people with similar conditions.

Can I experience withdrawal symptoms when stopping medical cannabis use?

Yes, some patients may experience withdrawal issues. However, your specialist will help to devise a treatment plan that will minimise any chance of withdrawal issues or side effects.

Cannabis withdrawal symptoms usually pass after 3 to 4 days and can include:

  • Headaches
  • Irritability
  • Insomnia or other sleep disturbances
  • Changes in appetite
  • Mood changes

Final thoughts

Like almost all medical treatment options, cannabis-based therapies may come with a few side effects. These side effects are usually very mild, and when prescribed and monitored by a specialist, most medical cannabis side effects can be effectively managed or avoided altogether.

If medical cannabis is something you are considering, feel free to head over to the Releaf eligibility checker. It takes less than 30 seconds, and you will instantly be advised whether you are potentially eligible for a UK medical cannabis prescription.

To learn more, check out our education and blog sections, or feel free to reach out to our team at any time.

It is important to seek medical advice before starting any new treatments. The patient advisors at Releaf are available to provide expert advice and support. Alternatively, click here to book a consultation with one of our specialist doctors.

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Sam North, a seasoned writer with over five years' experience and expertise in medicinal cannabis, brings clarity to complex concepts, focusing on education and informed use.

Our articles are written by experts and reviewed by medical professionals or compliance specialists. Adhering to stringent sourcing guidelines, we reference peer-reviewed studies and scholarly research. View our editorial policy.

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