Medical Cannabis vs CBD — What's the Difference?

CBD products and prescribed medical cannabis are both derived from the cannabis plant, but they are regulated differently, contain different active compounds in different quantities, and serve different clinical purposes. Confusing the two is common among patients exploring their options for the first time, and the distinction matters significantly in legal and clinical terms.

What Is CBD?

Cannabidiol (CBD) is a naturally occurring compound found in the cannabis plant. In the UK, CBD products are legal to sell as food supplements or cosmetics, provided they meet specific conditions set by the Food Standards Agency (FSA) and the Medicines and Healthcare products Regulatory Agency (MHRA).

Legal CBD products must contain no more than 1 mg of THC (tetrahydrocannabinol) per container, regardless of the size of the product. This threshold is set at a level considered to produce no psychoactive effect. CBD products do not require a prescription and are widely available in health food shops, pharmacies, and online.

It is worth noting that the CBD supplement market in the UK is not uniformly well-regulated at point of sale. Independent testing has found that some products on the market contain less CBD than labelled, or more THC than is legally permitted. Patients choosing OTC CBD products should look for those with independently verified certificates of analysis.

What Is Prescribed Medical Cannabis?

Medical cannabis in the UK refers to cannabis-based medicinal products (CBMPs) that have been prescribed by a specialist clinician holding the appropriate authority to prescribe Schedule 2 controlled drugs. These products may contain significant quantities of THC, CBD, or both, depending on the clinical indication and the prescribing decision.

Unlike OTC CBD products, prescribed medical cannabis is a controlled drug under the Misuse of Drugs Regulations 2001. It can only be legally obtained with a valid prescription from an authorised specialist, dispensed by a registered pharmacy. Possession without a valid prescription constitutes a criminal offence.

To find out whether you might be eligible for a prescription, see our guide on how to get medical cannabis in the UK.

The Role of THC

THC is the compound primarily responsible for the psychoactive effects associated with cannabis. It is also thought to play a role in the therapeutic effects of medical cannabis for certain conditions, either independently or in combination with CBD and other cannabinoids.

OTC CBD products, by law, contain negligible THC. Prescribed medical cannabis products may contain a meaningful therapeutic dose of THC, and it is often the presence of THC — or a specific THC-to-CBD ratio — that differentiates a prescription product from an OTC supplement in clinical terms.

This distinction is clinically significant for conditions such as chronic pain, PTSD, and sleep disorders, where the evidence for THC-containing products is more developed than the evidence for CBD alone.

Why a Patient Using CBD Might Need a Prescription

Many patients arrive at licensed clinics having already tried OTC CBD products without sufficient benefit. There are several reasons why CBD alone may not address a patient's needs:

• The dose of CBD in OTC products is frequently lower than doses used in clinical studies.
• OTC products contain no therapeutically significant THC, which may be necessary for certain conditions.
• Product quality and consistency in the OTC market varies considerably.
• Some conditions may respond better to specific cannabinoid ratios that are only achievable through prescription products.

None of this means OTC CBD is without value for some patients. For mild symptoms, or for patients who are not eligible for a prescription, CBD supplements may provide meaningful relief. The point is that CBD and medical cannabis are not interchangeable, and a patient who has not responded to OTC CBD should not conclude that cannabis-based treatment in general will not work for them.

Conditions Where the Distinction Matters Most

For certain conditions, the evidence base distinguishes clearly between CBD-only and THC-containing products. Epilepsy, for example, has two MHRA-licensed CBD-based medicines (Epidyolex) used within the NHS, but these are prescribed pharmaceutical products, not food supplements, and are used under specialist supervision. For adult conditions such as chronic pain, anxiety, and multiple sclerosis-related spasticity, most clinical guidance relates to products containing THC, not CBD alone.

Patients should be cautious about self-treating with OTC CBD for serious or chronic conditions without also seeking medical advice. CBD supplements are not a substitute for clinical assessment.

Regulatory Oversight

Prescribed medical cannabis sits within a well-defined regulatory framework. Clinics prescribing medical cannabis must be registered with the relevant national regulator — the Care Quality Commission (CQC) in England, Healthcare Improvement Scotland in Scotland, or Healthcare Inspectorate Wales in Wales. Prescribing clinicians must hold the appropriate specialist qualifications. The products themselves must meet pharmaceutical manufacturing standards.

OTC CBD food supplements are regulated by the FSA as novel foods. This means manufacturers must submit safety data before products can be lawfully sold, but the regulatory burden is lower than for medicines, and enforcement is inconsistent in practice. In short: prescribed medical cannabis is subject to medicines regulation; OTC CBD is subject to food supplement regulation. These are meaningfully different standards.

Frequently Asked Questions

Is CBD legal in the UK?

Yes, CBD products are legal in the UK when sold as food supplements or cosmetics, provided they contain no more than 1 mg of THC per container. They do not require a prescription. However, quality and accuracy of labelling varies, so look for independently tested products.

Do I need to see a doctor to use CBD products?

No. OTC CBD food supplements can be purchased without a prescription. However, if you are using CBD to manage a chronic or serious medical condition, inform your GP, particularly if you take other medications, as CBD can interact with certain drugs including blood thinners and some anticonvulsants.

Why might CBD not be enough for my condition?

OTC CBD products contain minimal THC and are often sold at lower doses than those used in clinical research. For conditions where the therapeutic effect may depend on THC or on a specific cannabinoid ratio, an OTC supplement may not provide sufficient benefit.

Can a GP prescribe medical cannabis?

In most circumstances, no. Medical cannabis can only be prescribed by a specialist clinician on the General Medical Council's Specialist Register. GPs may refer patients to a specialist, but they cannot initiate a medical cannabis prescription themselves in routine practice.

Will taking CBD show up on a drug test?

Standard workplace drug tests typically screen for THC metabolites, not CBD. A high-quality OTC CBD product containing no more than the legal THC limit is unlikely to cause a positive result at normal doses. However, this cannot be guaranteed, particularly with high-dose use or inaccurately labelled products.