11 min read
Hannah Clark
The first question that most new patients have (often before even reaching out to a medical cannabis clinic) is -
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.
Key takeaways
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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.
Both THC and CBD are classed as cannabinoids, and both offer patients alternative options for managing their symptoms. However, they do differ in some specific ways, with side effects being one of them.
Products containing more than 1 mg of each controlled cannabinoid 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 research suggests it to be an effective therapeutic option for 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Changes in mood (e.g. feeling more relaxed or socially withdrawn)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)
Other possible side effects, according to the NHS (2022), may include:
Decreased appetite
Diarrhoea
Feeling sick
Weakness
Mood changes
Dizziness
Feeling very tired
Feeling high
Hallucinations
Suicidal thoughts
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.
CBD products are allowed to be sold OTC in the UK, as long as each container has no more than 1 mg of each controlled cannabinoid.
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.
While exceedingly rare, there can be a few severe reactions to medical cannabis. Some of these can include:
Hallucinations
Panic attacks
Suicidal thoughts
Allergic reactions
Contact your prescribing specialist right away if you experience any rare or unwanted side-effects from your treatment, or call 999 in an emergency.
They can, but 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. 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.
Yes. Prescribed CBPMs, particularly those containing THC, can affect your ability to drive safely. Despite being legal in the UK, driving while impaired by medical cannabis is an offence, as it is with any other prescribed medication.
Patients are advised to consult their specialist if they are unsure whether a medication might affect their driving.
Before you can be prescribed medical cannabis treatment (or any prescription medicine) your specialist doctor will need a full list of medications you are currently taking to understand how best to proceed with your medical cannabis prescription.
All medicines are made up of chemicals that can react with the chemicals of other medications, leading to unexpected or unwanted side effects. When putting your medical cannabis treatment plan together, your specialist will take your current medications into account and advise on what medicines should not be taken with CBD or THC, depending on your proposed treatment.
Medical cannabis is not a cure-all for when other treatments have failed, but a complementary or alternative option for those who have not found relief through typical treatment options.
As such, and considering the side effects we have discussed above, it should not be a surprise that there are instances where medical cannabis is not a suitable treatment for the patient.
These instances mostly relate to psychiatric disorders such as:
Schizophrenia
Psychosis
Some studies have shown that THC can make these conditions worse, and as such, it would not be in the best interest of the patient to prescribe medical cannabis treatments.
In the vast majority of cases, 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.
The short answer is yes - in fact, medical cannabis 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.
Different medicines can affect people differently, and the side effects we have discussed are those that have been commonly observed.
If you experience side effects to your medication not listed above, you should inform your prescribing specialist. You can also report side effects through the MHRA Yellow Card Scheme.
Always follow the dosing and administration instructions of your prescribing specialist. Most new patients will be instructed to titrate their cannabis-based medication, which involves starting with a low dose and slowly increasing the dose size until the desired therapeutic effect is achieved.
Yes, both CBD and medical cannabis products containing THC may help some patients with anxiety symptoms, although research is still limited. Read more over at our medical cannabis for anxiety page.
Prolonged cannabis use without supervision can cause some problems, which is why following the advice and guidance of your prescribing specialist, and reporting back any sudden changes or reactions is essential.
The potential side effects of prolonged 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.
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.
For the most part, cannabis withdrawal is not considered severe, but this will depend on how frequent and heavy an individual's use is and whether they gradually reduce taking cannabis or stop completely.
The timeline for cannabis withdrawal can also vary per person, but symptoms usually start 24 to 48 hours after stopping, peak at days 2 to 6, and some can last 3 weeks or more in heavy users. Common withdrawal symptoms of cannabis include:
Headaches
Irritability
Insomnia or other sleep disturbances
Changes in appetite
Mood changes
The effects of cannabis on mental health can vary depending on the condition and how cannabis is being taken. Prescribed medical cannabis for mental health conditions may help some patients when taken as instructed and overseen by a specialist.
Self-medicating with cannabis is an entirely different story. Without a specialist to oversee titration, frequency, and side effects, cannabis can have adverse effects on mental health.
While most of the common side effects are mild and transient, no medicine is risk-free.
As we’ve mentioned above, in rare cases, allergic reactions can occur from medical cannabis, and some patients may even experience hallucinations and panic attacks as high levels of THC can induce feelings of anxiety, paranoia, or panic in some people.
However, when prescribed and monitored by a specialist doctor, these side effects can often be avoided. Always consult with your prescribing specialist if you are ever concerned about potential or unwanted side effects of your treatment.
Cannabis hyperemesis syndrome (CHS) is a gastrointestinal condition associated with taking cannabis frequently and over a long period. The symptoms of CHS typically appear within 24 hours of last cannabis use and include:
Recurrent nausea
Severe vomiting
Intense abdominal pain
CHS can potentially cause other complications, such as the erosion of enamel from frequent vomiting, dehydration, and in rare cases, heart rhythm abnormalities or seizures.
Yes, in some cases stopping medical cannabis can cause some adverse effects, commonly referred to as cannabis withdrawal. Symptoms may include headaches, dizziness, irritability, and sleeping difficulty.
If you are concerned about how stopping your cannabis treatment will affect you, speak with your prescribing specialist for advice.
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 you have a qualifying condition and 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.
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