SN instructed patient/ caregiver about Baclofen.That it is a muscle relaxer and an antispastic agent. SN instructed to Get emergency medical help if you have signs of an allergic reaction to baclofen such as: hives; difficult breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have: weak or shallow breathing; confusion, hallucinations; or a seizure (convulsions). Common baclofen side effects may include: drowsiness, dizziness, weakness, tired feeling; headache; sleep problems (insomnia); nausea, constipation; or urinating more often than usual.