Cannabis-based Medicinal Products

Cannabis-based medicines (CBMs) have been used for a variety of therapeutic purposes, with variable levels of evidence with regard to efficacy.

CBMs contain cannabinoids derived from the cannabis plant, including delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), or a combination of THC and CBD. Synthetic cannabinoids for medicinal use mimic the effects of specific cannabinoids such as THC.

THC is the constituent of cannabis that causes the 'high', whereas CBD is not intoxicating at typical doses. THC and CBD have contrasting mechanisms of action and therapeutic indications. THC carries a higher risk of adverse events compared with CBD^[1].

Since 1 November 2018, cannabis-based products for medicinal use (CBPMs) can be prescribed across the UK, but only by doctors on the relevant Specialist Register of the General Medical Council (GMC)^[1].

There is a wide range of over-the-counter (OTC) preparations of CBM available. Most of the evidence for beneficial effects is derived from studies of pure, pharmaceutical-grade CBM at relatively high doses. Relatively few studies have examined the effect of OTC CBM preparations, or of CBM at low doses. Therefore there is currently little evidence that OTC CBM preparations have health benefits, and their safety has not been investigated^[2].

Indications

National Institute for Health and Care Excellence (NICE) recommendations^[3]

Intractable nausea and vomiting

• Nabilone as an add-on treatment for adults with chemotherapy-induced nausea and vomiting which persist with optimised conventional antiemetics.
• When considering nabilone for adults with chemotherapy-induced nausea and vomiting, take into account potential adverse drug interactions - for example, with central nervous system depressants and other centrally active drugs.

Chronic pain
Cannabis-based medicinal products (nabilone, dronabinol, delta-9-tetrahydrocannabinol (THC), and combination cannabidiol (CBD) with THC) are not recommended for managing chronic pain^[4].

NICE recommends that none of the following should be offered to manage chronic pain in adults:

• Nabilone (a synthetic cannabinoid)
• Dronabinol (a synthetic form of THC)
• THC (delta-9-tetrahydrocannabinol)
• A combination of cannabidiol (CBD) with THC.

Adults who started cannabis-based medicinal products to manage chronic pain in the NHS before the NICE guidance was published (November 2019) should be able to continue treatment until it is considered appropriate to stop.

A Cochrane review found that the potential benefits of CBMs for chronic neuropathic pain might be outweighed by their potential harms. The quality of evidence for pain relief outcomes was limited, partly because of small sample sizes^[5].

Spasticity

• Offer a four-week trial of THC:CBD spray to treat moderate-to-severe spasticity in adults with multiple sclerosis (MS), if other pharmacological treatments for spasticity are not effective.
• After the four-week trial, continue THC:CBD spray if the person has had at least a 20% reduction in spasticity-related symptoms.
• Treatment with THC:CBD spray should be initiated and supervised by a physician with specialist expertise in treating spasticity due to MS.

Severe treatment-resistant epilepsy
NICE has published technology appraisal guidance on cannabidiol with clobazam for treating seizures associated with Lennox-Gastaut syndrome^[6]and Dravet syndrome^[7].

Other uses
Although benefits have been claimed for treating other conditions, evidence regarding benefits and risks is either limited or not supportive. A Cochrane review found no convincing, unbiased, high-quality evidence suggesting that nabilone is of value in treating people with fibromyalgia. The tolerability of nabilone was low in people with fibromyalgia^[8].

Prescribing^[3]

Initial prescription of cannabis-based medicinal products (excluding nabilone, THC:CBD spray (Sativex®) and medicines not classed as controlled drugs, such as cannabidiol, must be made by a specialist medical practitioner (a doctor included in the register of specialist medical practitioners (the Specialist Register) - section 34D of the Medical Act 1983^[9].

The specialist medical practitioner should also have a special interest in the condition being treated. The GMC have provided information for doctors on cannabis-based products for medicinal use^[10].

For children and young people under the care of paediatric services, the initiating prescriber should also be a tertiary paediatric specialist.

Shared care^[3]

After the initial prescription, subsequent prescriptions of cannabis-based medicinal products may be issued by another prescriber as part of a shared care agreement under the direction of the initiating specialist prescriber, if:

• Shared care is appropriate and in the person's best interest.
• The person's clinical condition is stable.
• The other prescriber is confident to make a fully informed prescribing decision about cannabis-based medicinal products.

Efficacy and safety of cannabis-based medicinal products should be monitored and evaluated, and doses should be adjusted by the initiating specialist prescriber as part of the shared care agreement.

A shared care agreement for a person prescribed a cannabis-based medicinal product should include:

• The responsibilities of all parties (the initiating specialist prescriber, the other prescriber(s), the patient, family and/or carers).
• The nature and frequency of monitoring and how this will be recorded.
• When treatment might be stopped - for example, if it is not effective.
• How suspected or known adverse reactions will be managed.
• How communication will be managed between the initiating specialist prescriber, the other prescriber, the patient, family and/or carers.
• How the treatment will be funded.
• How care will be maintained when the patient, initiating specialist prescriber or other prescriber moves location (including transition to adult services).

Prescribing issues^[3]

When prescribing and monitoring cannabis-based medicinal products, take into account:

• Current and past use of cannabis (including any OTC and online products).
• History of substance misuse including the illicit use of cannabis.
• Potential for dependence, diversion and misuse (in particular with THC).
• Mental health and medical history, in particular, liver impairment, renal impairment, cardiovascular disease.
• Potential for interaction with other medicines - for example, central nervous system depressants and other centrally active drugs, antiepileptics and hormonal contraceptives.

Pregnancy and breastfeeding (breastfeeding is a contra-indication for Sativex® and nabilone; there is limited evidence on the safety of cannabis-based medicinal products during pregnancy and breastfeeding).

When prescribing cannabis-based medicinal products for babies, children and young people, pay particular attention to the:

• Potential impact on psychological, emotional and cognitive development.
• Potential impact of sedation.
• Potential impact on structural and functional brain development.

When prescribing cannabis-based medicinal products, advise people to stop any non-prescribed cannabis, including OTC, online and illicit products.

Prescribers should record details of treatment, clinical outcomes and adverse effects for people prescribed cannabis-based medicinal products, using local or national registers if available. NICE have provided guidance on controlled drugs^[11]. 

Supporting shared decision making^[3]

Before prescribing cannabis-based medicinal products, discuss with people:

• The potential benefits and harms, including any risk of dependence or interaction with other medicines.
• The licensing status of the medicines.
• How long they might take the medicine.
• How long it will take to work.
• What it has been prescribed for and how to take it.
• How it may affect their ability to drive^[12].
• The need to seek advice before travelling abroad about the legality of cannabis-based medicinal products in other countries^[13].
• The importance of not allowing others to use the prescribed medicine.