Doctors will be able to prescribe cannabis products to patients from November 1, the home secretary Sajid Javid has announced.
The new rules apply to England, Wales and Scotland, and follow several high-profile cases, including that of young epilepsy sufferers Alfie Dingley and Billy Caldwell, whose conditions appeared to be helped by cannabis oil.
Setting out the new regulations regarding cannabis-based products for medicinal use, Mr Javid said: "This brings these products explicitly into the existing medicines framework.
"These regulations are not an end in themselves. The ACMD (Advisory Council on the Misuse of Drugs) will be conducting a long-term review of cannabis and the National Institute for Health and Care Excellence (Nice) has been commissioned to provide advice for clinicians by October next year.
"The government will monitor the impact of the policy closely as the evidence base develops and review when the ACMD provides its final advice."
From October 17, Canadians will also be able to access cannabis more easily.
The country will make it legal to buy cannabis from licensed shops supplied by government regulated companies.