Baclofen

Skeletal muscle relaxants and spasmolytics
Skeletal muscle relaxants and spasmolytics
High alert
An error with this medicine can cause serious harm: double checks and protocols are used.

A GABA-B agonist that eases spasticity from multiple sclerosis or spinal cord injury, by mouth or into the spinal fluid through a pump.

Updated Nov 1, 2026

Quick facts

Group: Skeletal muscle relaxants and spasmolytics
Target: GABA-B receptor (GABA-B1 subunit)
Used for: Spasticity from multiple sclerosis
Key effects: Drowsiness · Confusion · Nausea
Monitor: Muscle tone · Kidney function · Intrathecal pump
ATC: M03BX01

No doses: the clinician sets them by the current guideline.

Mechanism of action

GABA-B receptor (GABA-B1 subunit)Baclofen

The figure shows baclofen bound to the extracellular domain of the human GABA-B receptor, where GABA itself binds.

Target in 3D: GABA-B receptor (GABA-B1 subunit). PDB structure 4MS4 (RCSB PDB, public domain). View the structure at RCSB PDB

Baclofen is a structural analogue of GABA that activates GABA-B receptors in the spinal cord and brain. Acting before and after the synapse, it hyperpolarizes neurons and reduces the release of excitatory transmitters from primary afferent terminals, so monosynaptic and polysynaptic spinal reflexes are damped. Spasms, clonus and rigidity fall without a direct effect on the muscle.

Baclofen activates GABA-B receptors in the spinal cord
Afferent terminals release less excitatory transmitter
Spinal reflexes that drive spasticity are damped
Less tone, clonus and painful flexor spasms

Indications

Spasticity from multiple sclerosis (flexor spasms, clonus, rigidity) Multiple sclerosis →
Spasticity from spinal cord injury and other spinal cord disease Spinal cord injury →
Severe spasticity of cerebral origin (e.g., cerebral palsy) by intrathecal pump, after a positive screening bolus Cerebral palsy →

Adverse effects

Common

Drowsiness (the most common), dizziness, weakness and fatigue
Confusion, headache and insomnia
Nausea, constipation and low blood pressure
Urinary frequency

Contraindications

Hypersensitivity to baclofen
The intrathecal solution must never be given intravenously, intramuscularly, subcutaneously or epidurally

Key interactions

Alcohol and other CNS depressants (benzodiazepines, opioids, sedatives): Additive sedation and respiratory depression
Antidepressants and antipsychotics: Listed by MedlinePlus as medicines to review; more drowsiness and confusion

What is monitored

Muscle tone, spasm frequency and function (spasticity is sometimes needed to stand or walk)
Kidney function
Sedation and mental state; seizure control and EEG in epilepsy
Intrathecal pump: refill dates, alarms and the catheter; a sudden need for much higher doses suggests a catheter problem

Administration and safety

Never stopped abruptly: oral baclofen is tapered; intrathecal therapy depends on refills being on time
Intrathecal baclofen is a high-alert route: only trained staff refill the pump, through the reservoir septum, never the catheter access port (risk of fatal overdose)
Screening bolus, dose changes and refills are done where resuscitation equipment is available
Strict aseptic technique at every refill; the intrathecal solution is not mixed with other medicines

Pregnancy and breastfeeding

There are no adequate studies in pregnancy. Newborns of mothers who took oral baclofen until delivery have had withdrawal (high tone, tremor, seizures).

Nursing care

Teach early withdrawal signs: return of spasticity, itching, low blood pressure and tingling
Extra vigilance in injuries at T6 or above (autonomic dysreflexia) and in patients who cannot communicate
Watch level of consciousness and breathing after a bolus, a refill or a dose change
Assess fall risk and warn about drowsiness, alcohol and driving

Pharmacokinetics

Absorption: Rapid and extensive by mouth; given intrathecally, it reaches effective spinal fluid levels with far lower blood levels
Elimination: Mainly by the kidney, unchanged; accumulates in kidney failure
Onset and duration: Intrathecal bolus: effect within about half an hour to an hour, lasting about 4 to 8 hours

Test yourself

Think of the answer, then tap the question to see it.

Which receptor does baclofen activate?

The GABA-B receptor (a G protein-coupled receptor), mainly in the spinal cord.

What can happen if an intrathecal baclofen pump runs empty?

Withdrawal: high fever, altered mental state, rebound spasticity and rigidity, rhabdomyolysis and even death.

Which organ clears baclofen, so its dose needs care when it fails?

The kidney (it is excreted largely unchanged).

What is checked before an intrathecal pump is implanted?

A positive response to an intrathecal screening bolus.

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Connections

← Back to the class: Skeletal muscle relaxants and spasmolytics

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - BACLOFEN injection (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - BACLOFEN tablet (DailyMed (U.S. National Library of Medicine), 2026); Baclofen: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.