Medicinal cannabis - a potted guide

2 November 2018

The government has announced that from 1 November, medicinal cannabis can be prescribed by specialist doctors. In this blog, we look at what is meant by medicinal cannabis, how legislation is changing and what this is likely to mean for people with MS.

What is cannabis?

Cannabis is a naturally occurring drug made from parts of the cannabis plant. It contains many different compounds which are known as cannabinoids.  The combinations and proportions of these can differ widely depending on the strain of cannabis plant and how the drug has been prepared.

The two cannabinoids which have been studied the most are tetrahydrocannabinol and cannabidiol.

Tetrahydrocannabinol (THC) is responsible for the psychoactive effect or ‘high' that is associated with cannabis use.

Cannabidiol (CBD) has anticonvulsant properties and there is good evidence that it can treat severe forms of childhood epilepsy. It does not have a psychoactive effect.  CBD is thought to modulate the effects of THC which is why the ratio of THC to CBD can be important.

What is medicinal cannabis?

Medicinal cannabis is used to refer to the use of cannabis for medical purposes rather than for recreational use.  This could cover anything from the raw herbal product through to drugs manufactured to pharmaceutical standards which have been tested in clinical trials and been approved by drug regulators for specific conditions.

What evidence is there for medicinal cannabis in MS?

Studies have investigated different preparations of medicinal cannabis in pill or spray form; these have shown that medicinal cannabis can help to treat certain MS symptoms such as spasticity and spasms, reduce central pain (feelings of burning, pins and needles or numbness) and may lessen frequent urination.

Just two small studies have looked at smoked cannabis in people with MS; both investigated aspects of spasticity.  A review of these studies concluded that they did not provide enough evidence to show whether smoked cannabis is effective or safe in MS.

Sativex is prepared from cannabis plants and contains THC and CBD in equal proportions.  It has been studied extensively in clinical trials and is licenced in the UK as an add-on treatment for spasticity where other drugs have failed.

Although Sativex can be prescribed, it is not considered to be a cost-effective treatment for the NHS in England, Scotland or Northern Ireland.  In Wales, it is considered cost-effective and is approved as an NHS treatment, although availability is still limited.

Cannabis oils

Cannabis oils are extracts from cannabis plants.  Unprocessed, they contain the same active ingredients as the plants, but the balance of compounds depends on the specific plants the oil has been prepared from.

No clinical studies have been carried out to show whether or not the cannabis oils commercially available in the UK have any benefits in MS.  Anecdotally some people with MS say they have found cannabis oils to be beneficial, whilst others have seen no effect. 

Cannabis is a controlled drug under the Misuse of Drugs Act 1971. Controlled drugs are assigned a Class and a Schedule.  The Class (A, B and C) broadly reflects potential for harm, and has legal implications, including penalties for inappropriate supply and possession.  Cannabis and many cannabis-based products are assigned to Class B under the Misuse of Drugs Act 1971. The changes do not affect the Class of cannabis.

Recognising that potentially harmful drugs do have medical benefit in specific cases, they are also assigned to a Schedule (1-5) which spells out how they can be prescribed and stored.

Cannabis is currently assigned to Schedule 1, the most restrictive category, for drugs which are considered to have no recognised medicinal benefit.  They cannot be prescribed or held legally with a prescription.


Sativex is assigned to the less-restrictive Schedule 4.  This means that Sativex can be prescribed in the UK with no restrictions on supply, recording, storage or destruction.

Cannabis oils

The cannabinoid CBD, is not a controlled substance under the Misuse of Drugs Act.  Cannabis oils containing CBD can be sold legally in the UK, providing they contain negligible amounts of THC and do not make any claims for medical benefit and are not sold as medicines.  

In response to several high-profile cases earlier this year, the Home Secretary ordered a two part review of the scheduling of cannabis.

The first part, carried out by the Chief Medical Officer, concluded that there was strong evidence of a therapeutic benefit of cannabis-based medicinal products and that medicinal cannabis should be available for prescriptions "under controlled conditions by registered practitioners".

The second part of the review was conducted by the Advisory Council on the Misuse of Drugs (ACMD).  This recommended that cannabis-derived medicinal products should be placed in Schedule 2 provided that the products met safety standards, which would allow them to be legally prescribed.  The review stressed that “cannabis-derived products can vary greatly in their composition, effectiveness and level of impurity. It is important that clinicians, patients and their families are confident that any prescribed medication is both safe and effective.”

The review also concluded that raw cannabis and cannabis preparations of unknown composition should not be given the status of medication and that there should be no change to the legal status of cannabis for recreational use.

The Home Secretary accepted these findings and has announced that medicinal cannabis will be re-assigned to Schedule 2.  From 1 November specialist clinicians will be able to legally prescribe cannabis-derived medicinal products to patients with an exceptional clinical need.

What will this mean?

There are three key points to this change:

1. Specialist clinicians

Only doctors on the Specialist Register of the General Medical Council will be able to prescribe these drugs; GPs will not be able to prescribe them.

2. Cannabis-derived medicinal products

One of the key issues is precisely what is meant by cannabis-derived medicinal products (CDMPs).

An interim definition has been drawn up which essentially says that a CDMP must contain cannabis, THC, or related chemicals and must be produced for medicinal use.  It should be produced to good manufacturing practice standards, should have a clear description of content and should not be taken by smoking.  

NHS England has provided interim guidance to clinicians and to members of the public. These will be replaced by a full guideline on cannabis-derived products for medicinal use which NICE (National Institute for Health and Care Excellence) is just beginning to develop.  This is expected to be published by October 2019.

3. Exceptional clinical need

There's been no extra detail on this point so it will be left to the specialist clinician to make this decision.  The changes do not limit the types of conditions that can be considered for treatment.  So far, the focus of attention has been on treating severe childhood epilepsy and severe chemotherapy-induced nausea and chronic pain.

What will this mean for people with MS?

In the short term, the reality is that these changes are unlikely to make it easier for people with MS to access medicinal cannabis.  In the longer term, it does represent an opening-up of official attitudes to cannabis as a medicine.

Reassigning medicinal cannabis to Schedule 2 will make it easier to evaluate it in clinical trials.  Across a wide range of health conditions,including multiple sclerosis, there is limited evidence on the benefits and safety of medicinal cannabis.  In parallel to the changes to to the legal status of medicinal cannabis, investigators are being encouraged to set up new studies to gain a better picture of short and long-term safety and effectiveness.

Sativex is currently assigned to Schedule 4, which means it can be prescribed legally, but cost-effectiveness considerations mean that it is not offered as an NHS treatment in most of the UK.  Changes to the legal status of medicinal cannabis are unlikely to affect this.

The MS Trust will continue to push for changes in regulation that enable people with MS to access the treatments they need. The first part of that is to ensure that the NICE Guideline for the management of MS includes equity of access to existing, proven treatments such as Sativex.  In the longer term, opening the door that enables appropriate prescription of cannabis grown to good manufacturing practice standards can only be a good thing.

Find out more

On this page