Six-year-old Alfie Dingley, from Kenilworth in Warwickshire, suffers up to 30 violent seizures a day.
His parents want to treat him with medical cannabis oil, which is illegal in the UK.
The Home Office said the drug “cannot be practically prescribed, administered or supplied to the public”.
A spokesperson added that it can only be used for research.
Alfie’s mother, Hannah Deacon, said “you’ve got to fight for your kids, I want to know that I’ve done everything I can”.
Read more at the BBC