Understanding THC levels in medical cannabis in the UK

While there is much work still to do in terms of how cannabis is viewed through the UK’s societal lens, the stigma, misinformation, and demonisation of the plant are slowly decreasing, and in their place, a more balanced conversation is emerging. One that treats THC not as a cultural symbol (or worse), but as a legitimate medicine with both promise and limits, to be prescribed thoughtfully and monitored with care.

That last point is extremely important. For patients to find the best therapeutic outcomes, in both the short and long term, it’s essential that there is not only clinical guidance and oversight, but also access to clear information about what THC levels mean in practice and how they differ across products.

Releaf’s world-class clinical team takes great care when prescribing, always aiming to match each patient’s health needs and goals with the right formulation and strength, so treatment is safe and genuinely supportive of quality of life.

You can find a complete overview of THC in our comprehensive THC guide, covering how it affects the body, therapeutic applications, possible side effects, and patient FAQs.

How do THC levels vary by product type?

THC levels in prescribed cannabis products can range from almost zero to more than 90%, depending on the format. 

But when most people, especially those new to medical cannabis, first consider THC levels, they are usually thinking about dried flower. This is still the most common format prescribed in the UK and often the starting point for patients. 

Medical cannabis flower options sit in the mid-range compared to other products, with strengths that can be adjusted by cultivar choice and how much is taken. Other prescribable medical cannabis product types in the UK include medical cannabis oils, THC vapes, and edibles. Soon ,we will see capsules and other oral preparations entering the market, broadening the range of options for patients who need different routes of administration.

Product type	Typical THC range	Notes
Flower	7 to 30%	Inhaled by vaporisation, most common format
Oils	5 to 25%	Allows for controlled sublingual dosing
Extracts / vapes	60 to 90%+	Includes distillates and isolates, highly concentrated
Edibles	Variable	Slower onset, longer duration of effect

THC levels in flower

THC percentages in cannabis flower have risen gradually over the past 30 years. Advances in indoor cultivation, selective breeding programmes, and refined growing techniques have driven cannabinoid concentrations far beyond what was typical in previous decades. What once counted as a “strong” strain now often sits in the mid-range by today’s standards.

While it is possible for cannabis cultivars to tip the 30% THC mark, it is quite rare and not often seen in the UK medical cannabis market. Most prescribed flower sits between 7% and 28% THC. 

Cultivars up to around 20% are considered low to moderate strength, while anything above 20% is generally classed as high THC percentage. Patients may be prescribed THC-dominant flower, CBD-dominant flower, or balanced varieties that combine both cannabinoids, depending on their condition and treatment goals.

At Releaf, patients under the age of 25 are usually capped at 21% THC. This is because the prefrontal cortex, the part of the brain responsible for decision-making and impulse control, does not fully develop until around 25 years of age, which makes younger patients more vulnerable to the effects of higher-strength cannabis.

In the UK, it is illegal to smoke any form of cannabis, legally prescribed or not. All medical cannabis flower must be taken through a dry herb vaporiser. 

For more detail on how high THC levels are defined, see our guide: What percentage is considered high THC?

THC levels in oils

Medical cannabis oils prescribed in the UK usually range from 5 mg/ml to 25 mg/ml THC, with some higher-strength formulations reaching up to 50 mg/ml. As with flower options, these products are available in THC-dominant, CBD-dominant, and balanced profiles, which allows clinicians to recommend the right ratio for each patient’s condition and treatment goals.

A key advantage of oils is the accuracy they offer. 

They are taken sublingually, meaning drops are placed under the tongue and absorbed through the soft tissues of the mouth. This method gives steadier absorption than swallowing alone and allows doses to be measured and adjusted carefully under clinical guidance.

Patients sometimes ask about the highest THC oil available in the UK, but in practice, prescriptions rarely exceed 50 mg/ml.

THC vapes

THC vapes are a two-piece design. One section is the cartridge, often called a “cart,” which holds the cannabis extract. The other is the battery, a small rechargeable unit that heats the extract and turns it into vapour. 

The extracts in THC vapes usually sit in the high THC (90 to 95%) range. While that figure might sound intimidating at first, these products are designed to be used in very small amounts, making them safe and manageable under medical guidance.

Vaping also offers patients a level of discretion and convenience that other forms may not, as devices are portable, odour-light, and provide rapid onset of effects. Because of their strength, vapes are generally prescribed for patients who need fast relief or who have not responded well to lower-strength products. Clinical oversight remains essential, and doctors always weigh a patient’s age, medical history, and current medications before recommending them.

THC levels in edibles

Medical cannabis edibles vary widely in strength. 

Many are formulated with 5% to 10% THC and CBD, while some specialised preparations can reach 25% or even 50% of both THC and CBD. 

The effects of edibles take longer to kick in, as the cannabinoids must pass through the digestive system before entering the bloodstream. This slower onset of 60 to 90 minutes is balanced by a longer duration, which can make edibles helpful for patients who need sustained relief over several hours.

Because of this delayed onset, careful dosing is important. 

Patients are usually advised to start with a lower amount and wait before taking more, so the full effects can be assessed safely.

How do UK doctors prescribe THC?

At Releaf, every THC prescription begins with a free medical cannabis eligibility checker. If you are found to be potentially eligible, you’ll be asked to:

• Create a Releaf login to access the Releaf Patient Platform.
• Provide consent for medical record retrieval through our secure NHS login tool, or upload a copy yourself.
• Book your initial consultation with one of our GMC-registered specialists.

During this first consultation, the specialist doctor will review your medical history, symptoms, and current treatments. If THC is considered a suitable treatment option, a provisional prescription is written and passed to our multidisciplinary team for approval. This extra step ensures every prescription is safe, compliant, and matched to your health needs.

Safeguards are always in place. Once approved and payment is confirmed, your medicine is dispensed and delivered to your door within 2 to 5 days through tracked mail.

What are the UK rules on prescribing THC?

Medical cannabis containing more than 0.2% THC was legalised in the UK in November 2018. 

Since then, only doctors on the GMC specialist register have been allowed to prescribe it, and always with strict clinical justification. In other words, legal levels of THC in the UK are over 0.2% THC when prescribed by a specialist. Recreational use is still against the law, and patients must carry their prescription in its original packaging with the prescription label clearly printed when travelling with their medicine.

NHS vs private prescribing

The NHS keeps its prescribing window extremely narrow. Access is limited to three conditions: severe epilepsy, chemotherapy-induced nausea and vomiting, or multiple sclerosis spasticity. 

For most patients, the NHS route is simply not a realistic option.

Private clinics offer broader access, but the process is no less rigorous. 

Every prescription is written by a specialist, reviewed for safety, and approved under medical regulation. This is where the majority of UK patients find THC treatment, particularly for conditions like chronic pain, mental health concerns, sleeping issues, neurological disorders, women’s health issues, gastroenterological conditions, and as a supportive therapy option for cancer patients.

How Releaf supports patients

At Releaf, patients meet GMC-registered specialists backed by a clinical team of more than 30 doctors. Every new prescription is checked by our multidisciplinary team to ensure it is safe and appropriate. 

Patients are also issued a medical cannabis card, which provides proof of prescription at work, during travel, or in conversations with law enforcement. All of this is managed through our bespoke Patient Platform, built to make the process simple. 

From booking consultations to tracking deliveries, everything is kept in one place. Patients can choose PAYG flexibility or Releaf+ membership (£39.99/month) with unlimited follow-ups, free repeats, free delivery, and member pricing. With support from Glass Pharms, patients also gain access to UK-grown cannabis produced with a continuous harvest system, reducing wait times and supply interruptions.

Frequently asked questions

What THC level is safe for medical use?

There is no single “safe” level for everyone. For most patients, flower between 7% and 20% THC is considered low to moderate strength, while products above 20% are classed as high THC. The right level depends on age, condition, and treatment history, which is why prescribing is always guided by a specialist. You can read more about safety and dosing in our THC guide.

What is the highest THC level prescribed in the UK?

Prescriptions above 30% THC are extremely rare. At Releaf, patients under the age of 25 are not prescribed products above 25% THC, as the prefrontal cortex continues developing until around 25 years of age.

Can I choose my THC strength?

No. THC levels are prescribed according to clinical need, not patient preference. Doctors consider medical history, symptoms, and existing treatments before deciding on the appropriate strength. That said, your prescribing specialist will work with you to find the most appropriate treatment options for your health needs.

How do THC:CBD ratios affect treatment?

CBD can help offset some of the side effects of THC, such as anxiety or rapid heart rate. Many prescriptions use balanced THC:CBD formulations to achieve symptom relief while minimising risks.

How can you find the right THC treatment in the UK?

Medical cannabis THC levels in the UK vary by product type, from lower-strength oils and flower to highly concentrated extracts. What matters most is not the number on the label, but how that strength is prescribed and monitored. At Releaf, every decision is guided by clinical history, age, and individual health goals, so treatment remains safe, effective, and tailored to each patient.

If you are considering medical cannabis, the first step is to understand whether you may be eligible. Check your eligibility with Releaf’s medical cannabis eligibility checker. It takes less than 20 seconds, is obligation free, and could be the first step towards finding relief and support for your condition.