Baclofen (Lioresal, Gablofen) is a GABA-B receptor agonist used as an antispasticity agent and muscle relaxant for spasticity associated with multiple sclerosis, spinal cord injury, and other upper motor neuron disorders. It is available in oral and intrathecal (direct spinal delivery via implanted pump) formulations. The intrathecal route is reserved for severe spasticity unresponsive to oral therapy. A critical safety warning: abrupt discontinuation of baclofen — especially intrathecal — can cause a life-threatening withdrawal syndrome including seizures, hallucinations, hyperthermia, and multi-organ failure. Baclofen must always be tapered slowly.
Baclofen
Uses & FDA Indications
Oral baclofen is FDA-approved for the alleviation of signs and symptoms of spasticity resulting from multiple sclerosis (MS), particularly for the relief of flexor spasms and concomitant pain, clonus, and muscular rigidity. It is also approved for spinal cord diseases including spinal cord injury, ALS, and other upper motor neuron disorders. Baclofen is generally most effective for spinal spasticity rather than cerebral (supraspinal) spasticity.
Intrathecal baclofen (ITB, Gablofen) is FDA-approved for severe spasticity of spinal and cerebral origin — including MS, spinal cord injury, cerebral palsy, and traumatic brain injury — in patients who have not responded adequately to oral antispasticity drugs or who experience intolerable side effects at oral doses sufficient to control spasticity.
Off-label uses include alcohol use disorder (limited evidence), trigeminal neuralgia adjunct, hiccups (singultus), gastroesophageal reflux disease (GERD — GABA-B receptors reduce transient lower esophageal sphincter relaxations), and chronic pain syndromes.
How It Works
Baclofen is a structural analog of gamma-aminobutyric acid (GABA) that selectively activates GABA-B receptors — a distinct receptor family from the GABA-A receptors targeted by benzodiazepines and barbiturates. GABA-B receptors are metabotropic (G-protein coupled) receptors whose activation inhibits adenylyl cyclase, increases potassium conductance (hyperpolarizing the neuron), and reduces calcium conductance at presynaptic terminals — collectively reducing neurotransmitter release.
In the spinal cord, GABA-B receptor activation at interneurons and at the presynaptic terminals of afferent sensory fibers reduces excitatory input to alpha motor neurons, thereby decreasing muscle tone, spasm frequency, and the exaggerated stretch reflexes characteristic of spasticity. Baclofen does not directly act on muscle tissue — its antispasticity effect is entirely centrally mediated at the spinal cord level.
The intrathecal route of baclofen administration exploits the drug's pharmacokinetics: because baclofen has limited lipid solubility, it penetrates poorly from the bloodstream into the CNS. Delivering it directly into the CSF via an implanted pump achieves spinal cord concentrations 10–100 times higher than equivalent oral doses, enabling dramatic antispasticity effect at fractional systemic doses — dramatically reducing sedation, weakness, and other dose-limiting side effects common with oral therapy.
WITHDRAWAL WARNING: Abrupt discontinuation or sudden decrease of intrathecal baclofen can be LIFE-THREATENING. Symptoms of baclofen withdrawal — hyperthermia, severe rebound spasticity, rhabdomyolysis, seizures, hallucinations, multi-organ failure — have resulted in patient deaths. ALL patients on baclofen (especially intrathecal) must have a plan for what to do if pump failure, catheter occlusion, or missed refills occur. Emergency baclofen or cyproheptadine should be immediately available.
Side Effects
Common
- Sedation and drowsiness — very common, especially at initiation and with dose increases; often dose-limiting for oral baclofen
- Dizziness and lightheadedness
- Weakness (generalized hypotonia) — too much spasticity reduction can impair ambulation in patients who rely on some spasticity for functional standing or walking
- Nausea
- Headache
- Confusion and cognitive impairment — particularly in elderly patients or at higher doses; can range from mild memory difficulty to frank encephalopathy
- Urinary frequency or retention — affects bladder function; relevant in MS patients with pre-existing bladder dysfunction
- Constipation
Serious
- Respiratory depression — at excessive doses or in overdose; risk amplified by concurrent CNS depressants
- Seizures — paradoxically, both overdose and withdrawal can cause seizures. Baclofen lowers the seizure threshold in overdose and withdrawal causes severe seizures
- Intrathecal catheter complications — catheter tip granuloma (inflammatory mass at catheter tip) can compress spinal cord; catheter migration, kinking, or disconnection causes loss of drug delivery and precipitates withdrawal
- Baclofen overdose — causes CNS depression, respiratory depression, bradycardia, hypotension, and coma. No specific antidote; supportive care. Physostigmine has been used investigationally but is not standard.
- Life-threatening withdrawal — see warning box above
Drug Interactions
| Drug / Class | Interaction | Clinical Significance |
|---|---|---|
| CNS Depressants (opioids, benzodiazepines, sleep aids, alcohol, antihistamines) | Additive CNS depression — excessive sedation, respiratory depression, impaired psychomotor function. Baclofen plus opioids is a particularly high-risk combination in overdose. | High — use caution; counsel patients about additive sedation and driving impairment |
| Antihypertensives | Baclofen can potentiate the hypotensive effects of antihypertensive medications, particularly in patients starting baclofen or increasing doses. | Moderate — monitor blood pressure; orthostatic hypotension risk |
| MAO Inhibitors | May increase CNS depressant effects of baclofen and risk of hypotension. Concurrent use generally avoided. | Moderate — avoid concurrent use |
| Tricyclic Antidepressants (TCAs) | Additive muscle weakness and hypotonia reported with baclofen and TCA combinations. Both can lower seizure threshold at higher doses. | Moderate — monitor muscle strength and sedation |
| Lithium | Case reports of hyperkinesia (increased involuntary movements) with baclofen-lithium combination in some patients. | Low-Moderate — monitor for movement disorders if combining |
| Morphine (intrathecal) | When both are delivered intrathecally (combined pump), there is risk of additive respiratory depression and hypotension. Requires very careful dose titration and monitoring. | High — specialized monitoring required in combined intrathecal therapy |
Warnings & Contraindications
Contraindications
- Hypersensitivity to baclofen
- Intrathecal injection is contraindicated in patients with infection at the injection site, active systemic infection, or conditions making implant unsafe (coagulopathy, etc.)
Withdrawal Syndrome — Critical Safety Information
Baclofen withdrawal is among the most dangerous drug discontinuation syndromes in clinical medicine, particularly for intrathecal formulations. The withdrawal syndrome can occur due to: pump malfunction (battery failure, motor failure), catheter complications (kinking, migration, disconnection, occlusion), missed pump refill appointments, or deliberate or inadvertent dose reduction.
Early signs of withdrawal include return of spasticity and itching. Advanced withdrawal manifests as fever, altered mental status, exaggerated rebound spasticity, and muscle rigidity progressing to rhabdomyolysis. Severe withdrawal causes autonomic instability, seizures, and can progress to multi-organ failure and death. The condition mimics sepsis, neuroleptic malignant syndrome, and malignant hyperthermia — misdiagnosis delays appropriate treatment (reinstatement of baclofen or benzodiazepines for bridge therapy).
All patients on intrathecal baclofen should have emergency plans, including what symptoms indicate withdrawal, what to do if pump alarms, and where to go for emergency pump evaluation.
Renal Impairment
Like atenolol, baclofen is primarily renally excreted. Approximately 70–80% of an oral dose is excreted unchanged in the urine. Patients with kidney disease accumulate baclofen to higher plasma levels, increasing risk of excessive sedation, confusion, and seizures. Dose reduction is required in renal impairment. In patients with severe renal impairment or on dialysis, use must be undertaken with great caution and careful monitoring.
Elderly Patients
Elderly patients are particularly susceptible to baclofen's CNS effects. Sedation, confusion, and cognitive impairment are more pronounced and more clinically significant in older adults. Falls risk is elevated substantially. Lower starting doses, slower titration, and closer monitoring are essential in patients over 65.
Check for baclofen interactions with opioids, benzodiazepines, and other CNS depressants.
Check Drug Interactions →Frequently Asked Questions
What happens if you stop baclofen suddenly?
Abrupt baclofen discontinuation — particularly from intrathecal pump delivery — can cause a life-threatening withdrawal syndrome. Symptoms emerge within hours to days and include: high fever (hyperthermia), severe rebound spasticity, muscle rigidity, rhabdomyolysis, confusion and hallucinations, seizures, autonomic instability (fluctuating blood pressure and heart rate), and multi-organ failure. Intrathecal baclofen withdrawal has been fatal. It can mimic and be confused with conditions including malignant hyperthermia, neuroleptic malignant syndrome, and sepsis. Oral baclofen withdrawal, though less severe than intrathecal, also causes dangerous rebound spasticity, anxiety, insomnia, hallucinations, and seizures. Baclofen should always be tapered slowly when discontinuing.
What is intrathecal baclofen (ITB) therapy?
Intrathecal baclofen (ITB) therapy delivers baclofen directly into the cerebrospinal fluid (CSF) via a surgically implanted programmable pump connected to a catheter in the intrathecal space. This route achieves baclofen concentrations in the spinal cord hundreds of times greater than what oral administration can safely achieve, while using only a small fraction of the oral dose — dramatically increasing efficacy for severe spasticity while reducing systemic side effects. ITB is indicated for severe spasticity that does not respond adequately to oral baclofen or other antispasticity agents. The pump reservoir must be regularly refilled by a healthcare provider, and the system requires ongoing monitoring for catheter tip granuloma, pump malfunction, and programming accuracy.
Is baclofen used for alcohol use disorder?
Baclofen has been studied as an off-label treatment for alcohol use disorder (AUD), based on GABA-B receptor pharmacology — GABA-B agonism reduces mesolimbic dopamine release and appears to reduce craving and alcohol consumption in some patients. Evidence remains mixed: some trials (particularly French studies) showed benefit while others did not, and a Cochrane review found insufficient evidence to recommend routine use. Baclofen is not FDA-approved for AUD. In France, it has received marketing authorization specifically for reducing alcohol consumption. It is sometimes used off-label in the US by addiction medicine specialists when approved AUD pharmacotherapies (naltrexone, acamprosate, disulfiram) are ineffective or not tolerated.