Specialist doctors in the UK will be able to legally prescribe cannabis-derived medicinal products by autumn, the home secretary has announced.
Those that meet safety and quality standards are to be made legal for patients with an "exceptional clinical need", Sajid Javid said.
As it is a devolved matter, it will require legislative change before it is enforced in Northern Ireland.
Legalisation follows high-profile cases involving severely epileptic children.
Many had previously been denied access to cannabis oil.
Others forms of cannabis will remain illegal.
Javid's decision was made after the chief medical officer for England, Prof Dame Sally Davies, and the Advisory Council on the Misuse of Drugs said patients with certain medical conditions should be given access to the treatments.
Their advice was part of a review into medicinal cannabis launched by the home secretary following an outcry over Billy Caldwell and Alfie Dingley being denied access to cannabis oil.
The parents of the boys, who have rare forms of epilepsy, say it controls their seizures.
The Home Office recently granted them licences to access the treatments.
Javid said: "Recent cases involving sick children made it clear to me that our position on cannabis-related medicinal products was not satisfactory.
"That is why we launched a review and set up an expert panel to advise on licence applications in exceptional circumstances.
Billy Caldwell's mother, Charlotte, said Mr Javid's announcement had been made on her son's 13th birthday.
"For the first time in months I'm almost lost for words, other than 'thank you Sajid Javid'," she said.
"Never has Billy received a better birthday present, and never from somebody so unexpected...
"But, crucially, my little boy Billy can now live a normal life with his mummy because of the simple ability to now administer a couple of drops a day of a long-maligned but entirely effective natural medication."
