CBD vs THC: What’s the difference, and is medical cannabis right for you?

How is CBD different from medical cannabis?

CBD vs medical cannabis: What’s the legal difference in the UK?

While both CBD oil and medical cannabis products come from the Cannabis sativa L. genus (cannabis and hemp plants), they fall under totally separate and distinct legal and regulatory frameworks in the UK (and most other countries).

Here in the UK, CBD products can be legally sold over the counter if they are derived from “industrial hemp” cultivars that produce less than 0.2% THC - and the products themselves contain no more than 1 mg of THC per container. 

So yes, while CBD is legal in the UK, it is definitely not the same as medical cannabis. These products are classed as ‘Novel Food Items’ rather than medicines, and they’re not prescribed or individually dosed by a doctor. They are also not subject to anywhere near the same level of regulatory scrutiny and oversight that prescribed cannabis medicines are. 

Is medical cannabis really that different from over-the-counter CBD?

Yes.

Medical cannabis can only be prescribed by a GMC-registered specialist doctor and is only available for patients who have not responded well to at least two conventional treatment options. These prescriptions may include CBD, THC, or a combination of both, depending on the patient's needs.

The key legal differences are the inclusion of THC, the requirement for a specialist prescription, and the strict regulatory controls around both marketing and clinical use. 

Medical cannabis products are regulated as unlicensed medicines. They are prescribed on a case-by-case basis, taking into account symptom history and how a patient has responded to conventional treatments. Unlike consumer CBD, they can contain levels of THC that exceed the legal limit for over-the-counter use. Both the way these medicines are prescribed and the way they’re talked about (including in all marketing) is tightly controlled. 

This isn’t part of the wellness industry. It’s clinical care, shaped by regulation and led by specialists.

So although both come from the same plant, choosing between CBD oil and medical cannabis is not simply a question of strength or preference. One is a supplement. The other is a medicine.

How do CBD and THC interact with your body’s endocannabinoid system?

Understanding how medical cannabis works means understanding the endocannabinoid system (ECS). 

This isn’t some fringe biological discovery. It is one of the most widespread regulatory networks in the human body, helping to maintain balance across systems that affects mood, memory, sleep, immune function, pain response, appetite - the list goes on.

The ECS is made up of three core parts:

• Endocannabinoids, which are chemical messengers made by the body;
• Receptors, known as CB1 and CB2, to which these messengers bind
• And enzymes, which build and break down those chemicals as needed.

CB1 receptors are found mostly in the brain and central nervous system. They help regulate mood, memory, pain perception, and how we respond to stress. 

CB2 receptors, on the other hand, are more active in the immune system and peripheral tissues. They are closely linked to inflammation and immune signalling.

How does CBD work compared to THC?

THC binds directly to CB1 receptors, mimicking a natural endocannabinoid called anandamide, often referred to as the “bliss molecule”. This is what gives THC its intoxicating, euphoria-inducing effects, and also explains its ability to help with pain, nausea, appetite loss, and muscle spasticity.

CBD behaves quite differently. It doesn’t bind strongly to CB1 or CB2 receptors. Instead, it influences how the system behaves. It slows the breakdown of endocannabinoids, gently increasing their activity. It also interacts with other receptors like serotonin, GABA, and TRPV1, which are involved in mood regulation, anxiety, and pain sensitivity.

Think of THC as a key that fits directly into a lock. CBD is more like a hand resting on the thermostat. It doesn’t take over, but it gently adjusts the settings. 

Both can have therapeutic effects, but they engage the system in distinct and complementary ways.

The therapeutic potential of CBD and THC

CBD and THC are the two most clinically relevant cannabinoids found in cannabis. While they’re often discussed together, their effects (and their roles as part of a clinical treatment plan) are totally separate. One does not replace the other. Instead, they offer different kinds of support, and in some cases, they work best when combined.

Understanding their potential means looking not at wild claims, but real life outcomes and clinical data. 

What is CBD prescribed for in the UK?

CBD is non-intoxicating and generally well tolerated. It’s often used where inflammation, overstimulation, or nervous system dysregulation plays a role.

Current evidence shows that CBD oil can help with:

• Epileptic seizures: Particularly in rare, treatment-resistant forms such as Dravet or Lennox-Gastaut syndrome
• Anxiety and depression: Through its effects on serotonin and GABA signalling
• Inflammatory conditions: Including arthritis, IBD, and chronic pain
• Sleep disturbances: Especially when linked to anxiety or pain
• Neurodegenerative disorders: Such as Parkinson’s disease, where CBD’s antioxidant and neuroprotective properties may help
• Skin conditions: Including psoriasis and eczema, due to its localised anti-inflammatory effects

For many patients, especially those new to cannabis-based treatments, CBD is the starting point. But it does not offer the full therapeutic range that some conditions require

What medical benefits does THC offer patients?

THC is often prescribed when symptoms are more persistent, more disruptive, or more resistant to standard treatment. It tends to come into play when gentler options, including CBD alone, have not been enough.

Prescription THC in the UK may be used for:

• Chronic pain: Including neuropathic pain and musculoskeletal conditions
• Appetite loss and nausea: Particularly in patients undergoing chemotherapy
• Muscle spasticity: Especially in conditions like multiple sclerosis
• Inflammatory conditions: Such as Crohn’s disease or autoimmune disorders
• Anxiety or PTSD: In specific cases, under close supervision
• Palliative support: To improve quality of life in later-stage or terminal illness

Because THC is intoxicating in certain doses, it is handled carefully. It can only be prescribed by a doctor on the GMC specialist register, and only when two or more conventional treatments have been tried without success. 

But when used appropriately, and with the right patient, it can make a meaningful difference - not just in managing symptoms, but in restoring a sense of control.

Can CBD and THC be taken together?

Yes. And in many cases, that’s exactly the point.

CBD and THC interact with the body in different ways, which is why they’re often prescribed in combination. CBD can soften the effects of THC, particularly its tendency to cause anxiety or overstimulation in some patients. This allows for symptom relief without unwanted intensity.

This relationship is part of what’s known as the entourage effect. It refers to the way cannabinoids and other plant compounds appear to work more effectively together than they do alone. The goal isn’t to amplify the effects, but to create a more balanced and tolerable result.

What that balance looks like depends on the individual. Some patients benefit from formulations that are rich in CBD with just a trace of THC. Others respond better to a more equal ratio, or one that is more THC-heavy. 

This is where specialist oversight matters - finding the right profile, at the right dose, for the right condition is essential for patients to find the best possible clinical outcomes.

Are there any risks or side effects from CBD or THC?

CBD and THC both have a strong safety profile, especially when compared to many conventional pharmaceutical options. But they are not without risks. Like any medication, there are side effects to understand

Their effects vary from patient to patient, and the dose, administration method, and patient’s health profile all play a role in how cannabinoids are tolerated. 

What works well for one person may be too sedating, too stimulating, or simply ineffective for another. This is why careful prescribing and regular follow-up are so important in medical cannabis treatment.

The side effects of CBD

The side effects of CBD are generally mild and short-lived. These can include:

• Drowsiness or fatigue
• Light-headedness
• Changes in appetite or weight
• Gastrointestinal discomfort, such as nausea or diarrhoea
  
  

CBD can also affect how certain other drugs are metabolised. If you’re taking medications that are processed by the liver (particularly those involving CYP450 enzymes) it’s important to speak to a clinician before adding CBD to your routine.

The side effects of CBD

THC side effects are more dependent on dose.

At lower levels, THC may help with pain, sleep, and appetite. At higher doeses, it can cause:

• Anxiety or paranoia
• Impaired memory or concentration
• Dry mouth or red eyes
• Increased heart rate
• Dizziness, especially when standing

There is also a small risk of developing tolerance or dependence with long-term THC use, though this is far less common in medical contexts where dosing is carefully managed by a clinical team.

The short version: yes, both CBD and THC can cause side effects. But they’re usually manageable, often temporary, and can often be avoided altogether with the right dose and clinical guidance.

Why choose THC over CBD?

That comes down to your reasons for taking therapeutic cannabis options. But you don't have to choose one over the other, medical cannabis is now legal in the UK.

CBD products have you covered if you're looking for a natural supplement to promote overall wellness. CBD has also been shown to:

• Reduce chronic inflammation
• Activate serotonin production, producing an anti-anxiety effect
• Help with sleep issues
• Lower addictive cravings for tobacco and opioids under certain conditions

Medical cannabis products can contain the same (or more) CBD, but offer the added therapeutic benefits related to THC:

• Pain relief
• Nausea reduction
• Appetite stimulation
• Muscle spasm reduction for conditions such as multiple sclerosis

The above lists are just a small subsection of the documented therapeutic benefits associated with CBD and THC. For a more in-depth write-up, check out our education section.

Is medical cannabis legal in the UK, and how do you get it?

Medical cannabis can be prescribed legally in the UK, but access depends on very specific criteria. You need a recognised medical condition, and you need to have tried at least two conventional treatments without adequate results.

Prescriptions must come from a specialist doctor on the General Medical Council register. 

These are not off-the-shelf products. They are prescribed, monitored, and adjusted with clinical oversight and tailored to your specific symptoms.

While NHS access does exist in principle, it is limited in practice. At the time of writing, prescriptions through the NHS are largely restricted to severe childhood epilepsy, nausea linked to chemotherapy, and muscle spasticity in multiple sclerosis.

For everyone else, access is usually through private clinics. 

At Releaf, we connect patients with our world-class clinical team, who specialise in cannabis-based medicine. If you are interested in learning more about how to start your own medical cannabis journey, head over to our medical cannabis eligibility checker - it takes just 20 seconds to complete and is totally cost-free.