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

How is CBD different from medical cannabis?

THC vs CBD at a glance

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

While both CBD oil and medical cannabis products come from Cannabis sativa L. (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 contain no more than 1 mg of each controlled cannabinoids, like THC and CBN 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, who usually looks for at least two treatments that haven’t helped. A specialist doctor will decide whether a potential patient who meets the above criteria can then start a medical cannabis treatment plan. 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 THC and CBD both come from the same plant and mother cannabinoid, CBGA, 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). 

The endocannabinoid system 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.

How does CBD work compared to THC?

THC binds directly to CB1 receptors, which help regulate mood, memory, pain perception, and how we respond to stress. It mimics 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, which are more active in the immune system and peripheral tissues. 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 suggests that CBD oil may 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 may be 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 who will decide if medical cannabis treatment is right for you.

But when used appropriately, and with the right patient, it may 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, for a whole host of conditions, including anxiety for instance. 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?

Like with any medication, there are side effects from CBD and THC 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 but 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 THC

THC side effects are more dependent on dose.

At lower levels, THC may help with pain, sleep, and appetite. At higher doses, 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.

Which is better, CBD or THC?

CBD and THC are not competing products when it comes to medical cannabis. The two cannabinoids have different mechanisms and in prescribed medicine they are often combined, depending on what treatment your clinician suggests.

A specialist doctor will consider what formulation suits each individual patient, and their assessment will look something like this:

• Past medical history

• Condition diagnosis

• Unmet needs and symptoms

• Multidisciplinary team review and approval of treatment 

• Medical cannabis selection

• Dosage and frequency

• Follow-up consultations

Two people with the same condition may end up on different formulations based on the above answers.

Over the counter CBD is sold as a food supplement, not a medication. Unlike medical cannabis oils, CBD oils are not matched to your dosage and cannabinoid content differs between products.

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 tried at least two conventional treatments without adequate results to be considered for treatment. A specialist doctor will assess if you are ultimately eligible.

Prescriptions must come from a specialist doctor on the GMC specialist 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 forms of 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.

CBD vs THC FAQs

Does CBD get you high?

CBD is a non-intoxicating cannabinoid that does not produce the feeling of being ‘high.’ The cannabinoid THC is psychoactive and may cause a euphoric feeling depending on dosage.

Will CBD fail a drug test?

CBD can stay in your system for days or even weeks. CBD is not screened for in drug tests, instead they look for THC. CBD isolates do not contain THC so shouldn't trigger a test. Full-spectrum CBD products can contain up to 1 mg of THC per container and may show up on a screening. Medical cannabis containing a mix of CBD and THC will show, driving while impaired even with a prescription is not a defence, you can find out more on our Legal Status FAQ.

Can you feel stoned on CBD?

CBD generally will not cause you to feel ‘stoned’ however one of its side effects is drowsiness.