The most common adverse reaction during treatment with baclofen is transient drowsiness (10-63%). In one controlled study of 175 patients, transient drowsiness was observed in 63% of those receiving baclofen tablets compared to 36% of those in the placebo group. Other common adverse reactions are dizziness (5-15%), weakness (5-15%) and fatigue (2-4%). Others reported:
Neuropsychiatric: Confusion (1-11%), headache (4-8%), insomnia
(2-7%); and, rarely, euphoria, excitement, depression, hallucinations, paresthesia,
muscle pain, tinnitus, slurred speech, coordination disorder, tremor, rigidity,
dystonia, ataxia, blurred vision, nystagmus, strabismus, miosis, mydriasis,
diplopia, dysarthria, epileptic seizure.
Cardiovascular: Hypotension (0-9%). Rare instances of dyspnea,
palpitation, chest pain, syncope.
Gastrointestinal: Nausea (4-12%), constipation (2-6%); and, rarely,
dry mouth, anorexia, taste disorder, abdominal pain, vomiting, diarrhea, and
positive test for occult blood in stool.
Genitourinary: Urinary frequency (2-6%); and, rarely, enuresis,
urinary retention, dysuria, impotence, inability to ejaculate, nocturia, hematuria.
Other: Instances of rash, pruritus, ankle edema, excessive perspiration,
weight gain, nasal congestion. Some of the CNS and genitourinary symptoms may
be related to the underlying disease rather than to drug therapy. The following
laboratory tests have been found to be abnormal in a few patients receiving
baclofen: increased SGOT, elevated alkaline phosphatase, and elevation of blood
The adverse experience profile seen with KEMSTRO™ was similar to that seen with baclofen tablets.
The central nervous system depressant effects of baclofen may be additive to
those of alcohol and other CNS depressants.