Get emergency medical help if you have signs of an allergic reaction to baclofen: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
severe drowsiness, weak or shallow breathing;
confusion, hallucinations;
itching, tingling, or twitching in your hands, arms, feet, or legs;
fever; or
a seizure.
Common baclofen side effects may include:
drowsiness, dizziness, weakness, tiredness;
headache;
sleep problems (insomnia);
nausea, constipation; or
urinating more often than usual.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Baclofen side effects (more detail)
