The Department of Health is warning a no-deal Brexit could have a severe impact on the health service.
Secretary-general Jim Breslin says work is ongoing to ensure the supply of medicines and medical devices is protected.
But he says it's important service-users are aware of any possible changes to services or procedures.
Mr. Breslin's warning comes in a letter to Hiqa, written in July and released under the Freedom of Information Act.
But Sinn Féin's health spokesperson, Louise O'Reilly, says more no-deal planning is needed: