[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Skeletal muscle relaxants and spasmolytics](https://durgical.com/en/pharmacology/classes/skeletal-muscle-relaxants-and-spasmolytics/) › Baclofen

# 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](https://durgical.com/en/pharmacology/classes/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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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](https://www.rcsb.org/structure/4MS4) · Drag to rotate · pinch to zoom

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 →](https://durgical.com/en/conditions/multiple-sclerosis/)
- Spasticity from spinal cord injury and other spinal cord disease [Spinal cord injury →](https://durgical.com/en/conditions/spinal-cord-injury/)
- Severe spasticity of cerebral origin (e.g., cerebral palsy) by intrathecal pump, after a positive screening bolus [Cerebral palsy →](https://durgical.com/en/conditions/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

### Serious (rare, important)

- Withdrawal after abrupt stopping (especially intrathecal): high fever, altered mental state, rebound spasticity and rigidity, which can progress to rhabdomyolysis, multiorgan failure and death
- Hallucinations and seizures after abrupt withdrawal of oral baclofen
- Intrathecal overdose: drowsiness, respiratory depression, ascending hypotonia, seizures and coma
- Worse seizure control in epilepsy

## 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

## Memory aid

«Baclofen = Back off GABA-B, Back off slowly»: it works on GABA-B, and stopping it suddenly (especially from a pump) is an emergency.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/baclofen/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**High alert**
An error with this medicine can cause serious harm: double checks and protocols are used.

## Connections

## Related drugs 4

- [Tizanidine](https://durgical.com/en/pharmacology/tizanidine/)
- [Dantrolene](https://durgical.com/en/pharmacology/dantrolene/)
- [Diazepam](https://durgical.com/en/pharmacology/diazepam/)
- [Botulinum toxin type A](https://durgical.com/en/pharmacology/botulinum-toxin-type-a/)

## Related conditions 3

- [Multiple sclerosis](https://durgical.com/en/conditions/multiple-sclerosis/)
- [Spinal cord injury](https://durgical.com/en/conditions/spinal-cord-injury/)
- [Cerebral palsy](https://durgical.com/en/conditions/cerebral-palsy/)

[← Back to the class: Skeletal muscle relaxants and spasmolytics](https://durgical.com/en/pharmacology/classes/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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d63af5f0-c275-480b-89b5-6cf1ad55ab63) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - BACLOFEN tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1b0f50c8-62e3-414d-96d3-5fd16e8043ab) (DailyMed (U.S. National Library of Medicine), 2026); [Baclofen: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682530.html) (MedlinePlus (U.S. National Library of Medicine), 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/baclofen/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/baclofen/