Home Secretary Sajid Javid has announced that specialist doctors in the UK will be able to legally prescribe cannabis-derived medicinal products.

Cannabis is currently a controlled drug as classified by the Misuse of Drugs Act 1971.

A follow-up to this law, the Misuse of Drugs Regulations Act 2001, placed it under Schedule 1, which is the category for substances with no medicinal value. And this is the schedule being considered by the review.

Cannabis plants are made up of more than 100 different cannabinoids, which have different impacts on the body and are concentrated to different extents in certain parts of the plant.

The most well-known of these are THC and CBD.

THC is the psychoactive cannabinoid - the one that recreational users use to get "high". CBD does not have this effect.

While almost all cannabinoids are controlled substances under the Misuse of Drugs Act, CBD - or cannabidiol as it is also known - is not.

For example, industrial hemp may be grown under licence in the UK. It is a strain of the cannabis plant that contains little or no THC, but does contain CBD.

Cannabis oil

The Home Office says that it can contain a maximum THC content of 0.2% and that the THC must not be easily separated from it.

Industrial hemp can be used for things such as building materials and clothing.

CBD oil can also be extracted from these plants and, as it is a legal cannabinoid, can be sold in the UK.

The oil has been thought to have some medicinal properties, including relieving inflammation, pain relief and reducing anxiety, although there have not been conclusive scientific studies on this.

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Personal use

In 2016, the Medicines and Healthcare products Regulatory Agency (MHRA) said that CBD products, if advertised for these medical purposes, needed to be licensed.

Licences for CBD oil as a medicine have not been granted yet but the products can still be sold as long as claims are not made about their medical benefits.

Holland and Barrett sells some CBD oils as food supplements.

The oil that has been in the news recently due to its use by those with epilepsy is cannabis oil, which has a higher THC content, and so, unlike CBD oil, is not usually allowed in the UK.

But Sativex, which is a 50-50 mix of THC and CBD produced in a lab, has been approved for use in the UK by the MHRA as a treatment for multiple sclerosis.

However, in 2014, the National Institute for Health and Care Excellence, which issues guidance to NHS doctors, gave the medicine "do not recommend" status, saying it was not cost-effective.

Sativex is a spray. Each 10ml bottle contains 90 doses and costs about £140.

Paul Hunt, from CBD product supplier Vsavi, said: "This ruling by the Home Secretary is very welcome and we hope that this is just the start of changing opinions and legislation of CBD products by authorities in the UK."