Education Understanding THC levels in medical cannabis in the UK

Understanding THC levels in medical cannabis in the UK

6 min read

Sam North

Understanding THC levels in medical cannabis in the UK


Tetrahydrocannabinol, more commonly referred to by its abbreviation THC, is the potently intoxicating component in cannabis that is responsible for the recreational ‘high’ so often attributed to the consumption of cannabis. But THC is more than just a recreational substance, and a growing body of evidence shows  is showing its therapeutic potential for a wide range of medical conditions.

Since the legalisation of medical cannabis came into effect here in the UK in November 2018, there has been a steady increase in the number of patients looking to access THC as a therapeutic aid. Now, with private clinics being able to provide medical cannabis through prescription (instead of just the NHS, which only prescribes medical cannabis for a very restricted range of specific medical conditions), THC based treatment options are becoming more widely available.

But the vast majority of these new prospective patients simply don’t know have the knowledge needed to understand what different THC levels mean and how they may affect their treatment. So, this guide is here to help them understand the basics of THC levels in medical cannabis.

Here, we will have a look at the range of THC levels that are available in medical cannabis, as well as explore the potential benefits and risks associated with this new complementary treatment option. But first…

What is THC?

THC is one of the two predominant cannabinoids (specifically phytocannabinoids) produced by the cannabis sativa L. genus. This family of plants includes both cannabis and hemp cultivars, but it is important to note that not all strains of cannabis contain a significant amount of THC, and hemp plants contain almost no THC at all.

The human body also produces cannabinoids, which are referred to as endocannabinoids. These are one part of the endocannabinoid system (ECS), which is the largest neurotransmitter system in the body, and is made up of the endocannabinoids, receptors CB1 and CB2 which are activated by cannabinoid interaction, and metabolic enzymes that synthesise and also break down the endocannabinoids. It plays an active role in regulating many of our bodily functions, including:

  • Inflammatory responses
  • Appetite
  • Mood and emotion
  • Memory
  • Sleep patterns
  • Immune system responses
  • Pain perception

The chemical structure of THC is remarkably similar to that of the endocannabinoid anandamide (also known as the "bliss molecule"), which activates the CB1 receptor. This is why when THC is administered, it can interact with this same receptor (with THC also having a weak affinity to CB2), resulting in both intoxicating and therapeutic effects.

Understanding THC levels

The concentration of THC in different medical cannabis strains and products can range from 0 to over 90%. Dried cannabis flower will sit in the 0 – 33% THC region for the most part, but medical cannabis extracts such as isolates, distillates, oils, tinctures, and edibles can have concentrations as high as 99%.

This huge variance is one of the main reasons why it is essential to consult with a medical professional or cannabis specialist before starting any treatment. To legally receive medical THC products here in the UK, you must receive a prescription from a registered medical cannabis practitioner, who will consider your medical condition, your medical history, and any other medication you may be taking. This is so they can determine the correct strength and ratio of THC-to-CBD for your individual needs, as well as ensure you are aware of the potential risks.

The potential therapeutic benefits of THC

THC (and medical cannabis more generally) should never be promoted or viewed as a ‘cure-all’ for any medical condition. It has been shown to offer certain therapeutic benefits when administered as a complementary treatment, which is why it is often prescribed alongside other medications.

The current state of research suggests that THC may be helpful in the treatment of:

Does THC come with any risks or side effects?

As with all medicinal treatment options, THC does come with certain risks and side effects.

The common side effects can include:

  • dry mouth
  • headache
  • muscle spasms or tremors
  • palpitations
  • increased heart rate

In high-dose situations, THC has been shown to have the potential to cause increased anxiety, paranoia, and even panic or psychotic episodes. It should also be noted that THC can interact with any other medication you may be taking, as it is metabolised by the same enzymes as some other medications.


Understanding the THC levels in medical cannabis is an essential part of achieving the right treatment for you, and it isn't the easiest thing to do.

When considering the potential benefits and risks of THC in a medical setting, it is clear that it should always be taken with a certain level of caution, and prescribed by a medical professional who can work out the correct dose for your individual needs. Only doctors who are registered and have experience in prescribing THC-based medical cannabis products should be consulted to ensure that you get the best possible outcome from your unique therapeutic needs.

Releaf understands that finding a doctor who is registered to prescribe medical cannabis can be difficult. That's why we offer online consultations with our specialist doctors, as well as a unique medical cannabis card for extra protection and access to the treatment you require. If you're interested in learning more about our services or getting access to medical cannabis treatment, get in touch and one of our team members will be happy to help.

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.

Further reading

The Continental Cannabis Guide: Medical cannabis-friendly countries

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Medical cannabis on holiday: The basics

Here at Releaf we understand that holidays should be about relaxation, but travelling with medical cannabis sounds like a stressful voyage. We’re doing what we can to absorb that stress so that you can soak up the sun, and so, we’ve designed a series of articles to cover the subject: medical cannabis on holiday. 

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How long does it take to feel the effects of THC oil?

The time it takes for you to feel the effects of THC depends on the methods of administration as well as your own physiology. Fortunately, there are fast and slow-acting options, as well as ways to take low or high doses in order to facilitate control over the way your body reacts to your medicine.

Editorial Team