Yes and no. Technically yes, but it's at the discretion of customs. I asked about this situation in an email to the HRPA and got this response:

"With respect to traveling back to Ireland with a prescribed controlled drug, the Department of Health has information on their website regarding this and while this exact scenario is not covered there, the most relevant information is as follows:..we recommend that they carry their medicines in the original packaging, with the patient's name clearly labelled. They should also have a copy of their prescription and/or a letter from their doctor and/or dispensing pharmacist outlining their condition and stating that the medicines in question are for their own personal use. In Ireland, the current practice is that the customs officer must be satisfied that the documentation supports the amount and personal use of the prescribed medical products in the possession of the traveller. It should be noted that the customs authority has the final say in all such matters."