A highly addictive drug used as a painkiller and to control epilepsy appears on a list of medications which are at risk in the event of a no-deal Brexit.
The inclusion of Lyrica, also known as Pregabalin, on the list of drugs that may be affected by supply shortages has prompted fears that people may risk their lives by getting the class C drug on the black market.
It comes days after drugs charity Extern warned that some people in Londonderry have suffered overdoses recently as a result of taking Pregabalin.
Alex Bunting, the director of Addiction NI which provides treatment and support to people who are dependent on alcohol or drugs, said: "There are those people who take Lyrica because it has been prescribed to them by their doctor and then there are those who take it illegally.
"There is an issue with people sharing or selling Lyrica to family and friends and there are those who get it from the black market.
"My concern would be that there will be people who, if they cannot get their medication from their GP, may turn to the black market or who may self-medicate.
"Either scenario would, of course, be extremely dangerous because you really have no idea what you're getting."
While officials are working tirelessly to reduce the impact of a no-deal Brexit on the health service, they have admitted they cannot give a guarantee that medication supply will not be affected.
Lyrica has been identified as a drug that may be affected, alongside treatments for cancer, diabetes and high blood pressure.
They were included on a list put together by online pharmacy E-Surgery, with drug suppliers already reporting shortages of some drugs, while the price of some medication is also spiking, making it more difficult for pharmacists to purchase them.
Northern Ireland has the highest prescription rate for Pregabalin in the UK.
A growing number of people also use the drug recreationally and it has earned itself the name 'Belfast Buds' as it gives users the sensation of being drunk.
Lyrica, an anti-epileptic drug also used to relieve chronic pain, was reclassified as a class C drug earlier this year after it was linked to the deaths of 33 people in 2017.
Belfast GP George O'Neill, who is also chair of Addiction NI, said there is a risk that more people may turn to the black market if they cannot access their medication through proper channels.
"This is obviously a dangerous thing to do," he said.
"However, in the past few years we have been dealing with an increasing number of shortages from the pharmaceutical industry. It's a worldwide problem, and the system has worked quite well. At the moment, there are so many unknowns and, in that sense, no-one can predict what is going to happen.
"So while there are concerns, it is just something that we are going to have to deal with.
"I do think there are likely to be problems, but I think they will be solvable problems."
Alliance Party health spokeswoman Paula Bradshaw said she is concerned at the knock-on effect on the health service and police should people turn to the black market for medication.
"Not enough has been done to warn people of the direct practical consequences of Brexit, which go well beyond trade," she said. "The strain placed on the health service and police, which are both already understaffed, will be extremely significant with knock-on consequences felt by everyone in their daily lives."
Earlier this week, the Department of Health issued fresh guidance about its preparations to ensure services run as smoothly as possible if the UK leaves the EU without an agreement.
It said: "No one can provide an absolute guarantee that there will not be any disruption to the supply of medicines and medical products should the UK leave the EU without a deal.
"Such an absolute guarantee could not be given in normal circumstances, regardless of EU exit.
"However, we can assure the public that we are working very hard with all stakeholders to plan and mitigate against any such disruptions."
Officials failed to say if any operations will have to be cancelled in the event of a no-deal departure from the EU.
The advice however continued: "Planning for EU exit has been developed to try and make sure that there is as little impact upon the health service as possible, to prioritise care for patients in emergencies and minimise disruption to routine patient care."