CBD stands for cannabidiol. It is the second most prevalent of the active ingredients of cannabis (marijuana). While CBD is an essential component of medical marijuana, it is derived directly from the hemp plant, which is a cousin of the marijuana plant. While CBD is a component of marijuana (one of hundreds), by itself it does not cause a “high.” According to a report from the World Health Organization, “In humans, CBD exhibits no effects indicative of any abuse or dependence potential…. To date, there is no evidence of public health related problems associated with the use of pure CBD.”

Cannabis plants are made up of more than 100 different cannabinoids, chemical compounds that act on cannabinoid receptors in cells that alter neurotransmitter release in the human brain. These have different impacts on the body and are concentrated to different extents in certain parts of the plant, the BBC reports.

The most well known of the compounds are tetrahydrocannabinol (THC) and cannabidiol (CBD).

In the UK, it is possible to get a prescription for oil made from CBD because it won’t get users “high”. By contrast, THC is a psychoactive chemical and is a controlled substance under the Misuse of Drugs Act 1971.

A 2017 report by the World Health Organisation (WHO) found that CBD could provide relief for a variety of debilitating conditions including Alzheimer’s disease, Parkinson’s, multiple sclerosis, cancer and diabetic complications, as well as general pain, anxiety and depression.

“There isn't enough evidence to say that the oil definitely does help with these things, nor that simply cramming some in a milkshake will do the slightest bit of good, just that doctors are optimistic about their research,” says lifestyle magazine The Street.

One recent study has also now linked CBD oil to healthy weight loss. The research, published in the journal Molecular and Cellular Biochemistry, linked the drug to three causes of “fat browning”, which turns the dangerous white fat associated with obesity and diabetes into hard-working brown fat cells. These actively aid weight loss by burning extra calories through thermogenesis, your body’s heat-production process.

What’s more, CBD “reduces the expression of proteins involved in creating new fat cells, and it boosts the number of mitochondria in your brown fat cells”, says Men’s Health. This could further increase their fat-stripping power, the scientists suggest.

However, it is important to note that licences for CBD oil as a medicine have not been granted yet, and manufacturers cannot make claims about their alleged medical benefits.

CBD oil can be used in a number of different ways, says health information site Verywell. “You can smoke it (typically in vape pens), take it in capsule form, use it sublingually (under the tongue), use oral sprays or drops, or apply it topically to your skin,” the site explains.

“A crystalline form of pure CBD is also available, and it’s generally taken sublingually.”

CBD is available in a range of products sold on the high street and online, including creams, oils, tinctures and edible treats such as gummy sweets.

As Business Matters notes, there is currently “a great deal of confusion around CBD oil UK law”, with the vast majority of cannabinoids listed as controlled substances under the Misuse of Drugs Act.

However, CBD is an exception and is completely legal in the UK, “provided it has been derived from an industrial hemp strain that is EU-approved”, says NetDoctor. These strains contain very little to no THC.

For CBD oil to be legal in the UK, it must contain no more than 0.2% THC, and the THC must not be easily separated from it. By contrast, cannabis oil, which has a higher THC content, is not usually allowed in the UK.

There is an exemption to this rule, the BBC reports. Sativex, a 50-50 mix of THC and CBD produced in a lab, has been approved for use in the UK as a treatment for multiple sclerosis.

And specialist clinicians are allowed to prescribe other cannabis-derived medicinal products under changes to the law that came into force in November.

However, medicinal cannabis is currently unlicensed - so it can only be prescribed if a patient has a need that cannot be met by licensed medicines.

One of the arguments against the use of the medication “is that there have not been satisfactory drug trials to prove its safety and effectiveness”, reports the BBC’s Debbie Jackson.

As a result, it is rarely prescribed, which has resulted in a number of high-profile cases of parents taking their children out of the UK in order to access treatment.

One such parent is Julie Galloway, who left Scotland with her severely ill seven-year-old daughter, Alexa, almost 12 months ago to live in the Netherlands.

“I feel like a refugee forced to live abroad to save my child,” Galloway told the broadcaster. “I want to come home but I am terrified the medication will be confiscated. I am struggling to pay for it and I know this can't go on forever.”