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What are cannabis-based medicines?

Cannabis-based medicines (CBMs) are medicines derived from cannabis that have been used for treating medical conditions. CBMs contain cannabinoids derived from the cannabis plant, including delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), or a combination of THC and CBD. THC is the constituent of cannabis that causes the 'high', whereas CBD is not intoxicating at typical doses. THC is more likely than CBD to cause side-effects.

Man-made (synthetic) cannabinoids are also available. They mimic the effects of specific cannabinoids such as THC.

What conditions can cannabis-based medicines be used to treat?

CBMs have been studied in a variety of different conditions but there is currently only evidence of benefit in a few conditions. Therefore only a few people are likely to get a prescription for medical cannabis. Currently, CBMs are only prescribed for the following conditions:

• Adults with nausea or vomiting caused by العلاج الكيميائي.

• People with muscle stiffness and spasms caused by multiple sclerosis (MS).

• Children and adults with rare, severe forms of الصرع.

Medical cannabis is only prescribed when other treatments have not worked or are unsuitable.

There is some evidence medical cannabis can help certain types of chronic pain (for example in fibromyalgia), though this evidence is not yet strong enough to recommend it for pain relief.

In the UK, currently, it may only be prescribed for pain as part of a clinical trial.

Nausea and vomiting caused by chemotherapy

Chemotherapy may cause a person to feel sick (nauseous) or vomit. Nabilone is a man-made (synthetic) CBM that can be prescribed by a specialist to help relieve these symptoms, but only when other treatments have not helped or are not suitable.

Muscle stiffness and spasms caused by multiple sclerosis

Nabiximols (Sativex®) is a CBM that is sprayed into the mouth. In the UK, it is licensed for people with MS-related muscle spasticity that has not improved with other treatments.

Severe treatment-resistant epilepsy

Epidyolex® is a highly purified liquid containing cannabidiol (CBD). It will not get you high, because it does not contain tetrahydrocannabinol (THC), the chemical in cannabis that makes you high. Epidyolex® can be prescribed for patients with Lennox-Gastaut syndrome or Dravet syndrome, which are both rare types of epilepsy.

What are the side-effects of cannabis-based medicines?

The risks of using CBMs containing THC (the chemical that gets you high) are not currently clear. Ongoing clinical trials are needed before they can be used safely. 'Pure' products that only contain CBD, such as Epidyolex®, do not carry these unknown risks linked with THC. However, most products will contain a certain amount of THC.

The main risks of THC cannabis products are:

• An increased risk of a psychotic illness such as الفصام.

• Dependency on the medicine (addiction). This risk is probably small when its use is controlled and monitored by a specialist doctor. The risk increases with increasing levels of THC.

Cannabis bought illegally off the street, with unknown quality, ingredients and strength, is the most dangerous form to use.

The other possible side effects of CBMs are:

• Poor appetite.

• إسهال.

• الشعور بالغثيان.

• Weakness.

• Change in behaviour or mood.

• الدوار.

• Feeling very tired.

• Feeling 'high'.

• Hallucinations.

• أفكار انتحارية.

Like many other medicines, CBMs can also affect how other medicines work. Always discuss possible interactions with a specialist. CBD can also affect how your liver works, so doctors would need to monitor you regularly.

How can you get a prescription for a cannabis-based medicine?

You cannot get a prescription for a CBM from a GP. A CBM can only be prescribed by a specialist hospital doctor. The specialist will advise trying other treatment options first, before considering a cannabis-based product. A prescription for medical cannabis would only be given when it was believed to be in your best interests, and when other treatments had not worked or were not suitable.

What else do you need to know?

Before being prescribed a CBM, the following should be discussed with you:

• The potential benefits and harms, including any risk of dependence or interaction with other medicines.

• The licensing status of the medicines.

• How long you 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 your ability to drive (see Further Reading below for the advice from the Department of Transport on drug driving and medicine.

• The need to seek advice before travelling abroad about the legality of cannabis-based medicinal products in other countries (see the UK Government's advice on travelling with medicine containing a controlled drug in the Further Reading section below).

• The importance of not allowing others to use the prescribed medicine.