Common Side Effects of Baclofen
The most common side effects of baclofen include transient drowsiness (affecting 10-63% of patients), dizziness (5-15%), weakness (5-15%), and fatigue (2-4%), with neuropsychiatric effects such as confusion (1-11%) also frequently reported. 1
Primary Side Effect Profile
Baclofen is a GABA-B receptor agonist commonly used for the treatment of spasticity. Its side effect profile includes:
Central Nervous System Effects
- Drowsiness/sedation: Most common side effect (10-63% of patients)
- Dizziness: Affects 5-15% of patients
- Weakness: Affects 5-15% of patients
- Fatigue: Affects 2-4% of patients
- Confusion: Affects 1-11% of patients
- Headache: Affects 4-8% of patients
- Insomnia: Affects 2-7% of patients
Gastrointestinal Effects
- Nausea: Affects 4-12% of patients
- Constipation: Affects 2-6% of patients
- Rarely: Dry mouth, anorexia, taste disorders, abdominal pain, vomiting, diarrhea
Cardiovascular Effects
- Hypotension: Affects 0-9% of patients
- Rarely: Dyspnea, palpitations, chest pain, syncope
Genitourinary Effects
- Urinary frequency: Affects 2-6% of patients
- Rarely: Urinary retention, dysuria, sexual dysfunction
Other Reported Effects
- Rash, pruritus, ankle edema, excessive perspiration, weight gain, nasal congestion
- Abnormal laboratory tests: Increased SGOT, elevated alkaline phosphatase, elevated blood sugar 1
Special Considerations
Withdrawal Risk
Abrupt discontinuation of baclofen can cause severe withdrawal symptoms including:
These withdrawal symptoms can be potentially life-threatening, particularly with intrathecal baclofen, where symptoms may include high fever, altered mental status, rebound spasticity, and muscle rigidity that can lead to rhabdomyolysis and multiorgan failure 3, 4.
Renal Impairment
Baclofen requires dose adjustment in patients with renal impairment as it is primarily excreted by the kidneys. Patients with severely reduced kidney function (eGFR <30mL/min/1.73m²) may need to avoid the medication or use significantly reduced doses 3.
Elderly Patients
The American Geriatrics Society advises using baclofen with caution in elderly patients due to increased risk of CNS effects including sedation, confusion, and dizziness 3.
Management of Side Effects
- Start with low doses and gradually titrate upward to minimize adverse effects
- Monitor for CNS effects particularly in elderly patients or those with renal impairment
- Treat constipation proactively as tolerance does not develop to this side effect
- Never abruptly discontinue - always taper slowly to prevent withdrawal symptoms
- Consider alternatives such as tizanidine if side effects are intolerable (though tizanidine has its own side effect profile) 5
Baclofen remains an important medication for managing spasticity, but careful monitoring and patient education about potential side effects are essential for safe and effective use.