The family is receiving legal aid for the action at the high court against the National Institute for Health and Care Excellence (Nice), which sets prescribing guidelines for the health service.
The high court judge paid tribute to the “dogged persistence” with which the Hugheses had sought “what they believe to be the best, and safe, treatment for their son and the rare and serious condition from which he suffers”.
Prof Harry Sumnall of Liverpool John Moores University said the review, if upheld, could provide welcome clarity over whether NHS doctors can prescribe medicinal cannabis. He remained mindful that high-quality evidence of its benefits was still lacking.
With regards to cannabis-based medicines available on the NHS for epilepsy, Nice recommends just Epidyolex for two rare syndromes of the condition. Because of European Medicines Agency recommendations, it must be taken in conjunction with Clobazam, a benzodiazepine that some parents have said can cause troubling side-effects including hallucinations and amnesia.
Charlie Hughes, 3, has a rare form of epilepsy called West syndrome, which is resistant to most forms of treatment and can cause him to have up to 120 seizures a day, according to his parents, Alison and Matt Hughes. With regular full extract cannabis oil, however, he experiences no more than 20 less severe seizures a day.
Cannabis has long been thought to have therapeutic properties. Cannabis products contain a substance called THC; the component that causes a medical high. In the UK there are laws regarding the amount of THC in cannabis products which are only legal if they contain less than 0.3% THC.
Containing less than 0.1% THC, pure cannabidiol (CBD), has been prescribed in certain circumstances, and through clinical trials has been shown to be effective in complex epilepsies, more specifically Dravet syndrome and Lennox Gastaut syndrome. These findings have been submitted with a view to gaining a licence. There is no evidence about the efficacy or safety of higher amounts of THC.
Cannabis oils available in the UK and on the internet are not regulated medicines so their contents and dosage will not be consistent. People must always speak with their specialist epilepsy consultant if they are considering any alternative treatment including cannabis oil.
The effects of cannabis on epilepsy have been under discussion for a number of years and the current interest in the case of Billy Caldwell has highlighted this even further.
NHS England said doctors would be able to prescribe Epidyolex from 6 January.
"Shockingly, to our knowledge, not a single prescription for the medicine with those two parts was issued on the NHS since the law was changed."
Mr Carroll added: "The law was changed in November 2018 so that specialist doctors could write a prescription for medical cannabis with the CBD and THC, even though they are unlicensed.
Medical cannabis campaigner Peter Carroll said it was "too little, too late" as he urged action towards making medicinal cannabis with CBD and tetrahydrocannabinol (THC) available for families in need.
Decisions on drug availability are devolved around the UK.