Prescription medicine Pregabalin has been classified as a Class C drug after being linked to 33 deaths in Northern Ireland.
The anti-epileptic drug, known by the brand name Lyrica or street name 'bud', can also be used to relieve nerve pain.
The recommendation to classify the drug was made by the Advisory Council for the Misuse of Drugs, in a letter to ministers in 2016 - which cited significant misuse warnings from the Health and Social Care Board.
The legislation change came into effect today - April 1.
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This means it is now illegal to possess Pregabalin without a prescription, with the maximum penalty for unlawful possession of the drug being two years in prison.
Selling or supplying Pregabalin can now carry a prison sentence of 14 years.
Social justice charity Extern has released a guide aimed at those struggling with a Pregabalin addiction when the drug isn't being prescribed for them and people who have a prescription, but who are overusing the drug.
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Speaking about the new guide, author Chris Rintoul, from Extern’s Drugs & Alcohol Consultancy Service, said: “Just because Pregabalin is a prescription drug, does not mean that it is not dangerous.
"In an ideal world, Pregabalin would only be used as, and how, it is prescribed.
"Unfortunately, however, and even with the introduction of today’s new legislation, the reality is that there are thousands of people in Northern Ireland, and many more globally, who will continue to use this drug who have not been prescribed it, or who will find themselves using it outside of their prescription limits.
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“It is vital therefore, that as a society, we do as much as we can to enable those people to reduce the risk of harm to themselves.
"That is why Extern, with the valuable support of the Public Health Agency, have created this frank and open guide.
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"It offers informed and non-judgemental advice, and I would urge anyone who is misusing pregabalin to visit www.extern.org and download a copy of the guide, or get hold of a copy from their GP. It could save their life.”
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