Cannabis-based medicinal products will be available in Northern Ireland from today.
The products can only be obtained if they have been prescribed by a specialist hospital doctor.
The Department of Health (DoH) says patients must have an unmet clinical needs.
The move follows a high profile campaign for the relaxation of regulations around cannabis-based products for medicinal use.
Billy Caldwell, 13, of Castlederg, Co Tyrone, hit the headlines during the campaign.
Earlier this year, he received national attention when his medicinal cannabis was confiscated by the Home Office after a trip to Canada to access the medication.
Billy suffers from a severe form of epilepsy and his mother Charlotte says medicinal cannabis products help to ease his symptoms.
She spent years campaigning for the law change.
The Home Office then gave him a short-term licence and the DoH issued an emergency licence to allow him access to cannabis oil medication.
Belfast Health Trust secured a licence to administer the medication to Billy at the Royal Victoria Hospital.
He was then given permission to receive the medication at his Castlederg home.
In early October, Home Secretary Sajid Javid announced a decision to reschedule the products, relaxing the rules around the circumstances in which they can be given to patients, after considering expert advice from a specially commissioned review
Charlotte said she wept happy tears at the move.
“What started out as a journey for me as Billy’s mummy to help my little boy has become something much bigger,” she said.
From November 1, cannabis-based products for medicinal use can be prescribed by specialist hospital doctors for their patients with an unmet clinical need.
In a statement, the DoH said: “It is important that prescribing decisions are taken by expert clinicians informed by evidence on quality, safety and effectiveness.
“Therefore, prescribing of cannabis-based products for medicinal use is restricted to clinicians listed on the Specialist Register of the General Medical Council.
“Cannabis-based products for medicinal use will not be available from General Practitioners.”
The department added: “It is important to note that the rescheduling of cannabis-based products for medicinal use does not pave the way towards legalising cannabis for recreational use.
“The penalties for unauthorised supply and possession will remain unchanged.”
Epilepsy Action deputy chief executive Simon Wigglesworth welcomed the move but said the current guidance “seems extremely restrictive”.
“Today’s change in the law should open the door for some children and adults with severe epilepsy to access potentially life-changing treatment,” he said.
“While this change is an important step forward, the guidance we have seen so far on how it will work in practice seems extremely restrictive.
“It suggests that cannabis-based medicines will only be an option for a very limited number of people with epilepsy - children with Dravet or Lennox Gastaut syndrome.
“Though this is welcome, there are children and adults with other complex and treatment-resistant epilepsy syndromes who could potentially also benefit.”