CBD is a chemical substance found in cannabis or hemp that has reported medical benefits, such as reducing stress, inflammation and insomnia.
It is legal in the UK as long as it does not contain THC, the active ingredient in cannabis which gets you high and is a controlled substance under the Misuse of Drugs Act 1971.
Despite a lack of rigorous scientific studies into the oil's benefits, people have reported it helps them with chronic pain conditions.
The size of the UK CBD market is believed to be £300m per year with 1.3m active users, according to the latest findings.
This is larger than the total UK Vitamin D (£145m) and Vitamin C market (£119m) combined.
he market is currently growing at a huge rate and is expected to be just short of £1bn by 2025.
This would be equivalent to the entire UK herbal supplement market in 2016.

However the NHS says on its website: "Many cannabis-based products are available to buy online, but their quality and content is not known. They may be illegal and potentially dangerous.
"Some products that might claim to be medical cannabis, such as 'CBD oil' or hemp oil, are available to buy legally as food supplements from health stores. But there's no guarantee these are of good quality or provide any health benefits."
Supplement manufacturers are now calling on the UK Government to clear up the legislation around CBD use.
“The benefits of CBD are now being better publicised as a huge volume of research is released across the globe,” says Paul Waite, founder of company New Leaf CBD.
“Our aim is to help bring these benefits to their customers by producing carefully researched and diligently tested CBD supplements.”