Baclofen: Uses, Dosage & Side Effects

What Is Baclofen and What Is It Used For?

Baclofen is a prescription medication belonging to the centrally acting muscle relaxant drug class. First synthesized in 1962 and introduced to clinical practice in the 1970s, baclofen was originally developed as an anti-epileptic agent. However, researchers quickly discovered that its most significant clinical effect was the reduction of muscle spasticity, and it has since become one of the most widely used antispastic medications worldwide. Baclofen is included on the World Health Organization (WHO) Model List of Essential Medicines, reflecting its importance in global healthcare.

Structurally, baclofen is a chlorophenyl derivative of gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the central nervous system. Unlike benzodiazepines, which act on GABA-A receptors in the brain, baclofen selectively activates GABA-B receptors located primarily on the presynaptic terminals of primary afferent neurons in the spinal cord. By binding to these receptors, baclofen hyperpolarizes afferent nerve terminals and reduces the release of excitatory neurotransmitters, particularly glutamate and aspartate. This results in the inhibition of both monosynaptic and polysynaptic spinal reflexes, leading to decreased muscle tone, reduced spasm frequency, and relief of painful muscle contractions.

Baclofen is indicated for the treatment of spasticity resulting from a wide range of neurological conditions. The most common indications include multiple sclerosis (MS), where demyelination of nerve fibers in the brain and spinal cord leads to progressive motor dysfunction and spasticity; spinal cord injuries, whether traumatic or disease-related, which disrupt the normal regulation of spinal reflexes; cerebral palsy, a group of permanent movement disorders arising from damage to the developing brain; and cerebrovascular accidents (stroke), which can result in upper motor neuron damage and subsequent spasticity in affected limbs.

Spasticity is characterized by velocity-dependent increases in muscle tone, meaning the faster a muscle is stretched, the greater the resistance. Patients typically experience involuntary muscle stiffness, painful spasms, clonus (rhythmic involuntary contractions), hyperactive deep tendon reflexes, and difficulty with voluntary movement. These symptoms can significantly impair mobility, activities of daily living, sleep quality, and overall quality of life. Baclofen addresses these symptoms by reducing the abnormal neural activity that drives spasticity, allowing patients greater freedom of movement and comfort.

Baclofen is available in two primary formulations. Oral baclofen is the most common form, available as 10 mg and 25 mg tablets taken multiple times daily. Oral baclofen is suitable for patients with moderate spasticity and is the initial treatment approach. However, because baclofen crosses the blood-brain barrier poorly, relatively high oral doses may be needed, which can cause systemic side effects such as drowsiness, weakness, and dizziness. For patients with severe spasticity who cannot tolerate adequate oral doses or who fail to respond sufficiently to oral therapy, intrathecal baclofen (ITB) offers a powerful alternative. Intrathecal baclofen is delivered directly into the cerebrospinal fluid via a surgically implanted programmable pump, typically placed in the abdominal wall. This route allows effective concentrations of baclofen to reach the spinal cord at doses approximately 100 times lower than oral doses, dramatically reducing systemic side effects while achieving superior spasticity control.

Intrathecal baclofen therapy was first approved in the late 1980s and has since become a well-established treatment for severe spasticity. The intrathecal solution is available in concentrations of 0.05 mg/ml (used for test doses), 0.5 mg/ml, 1 mg/ml, and 2 mg/ml. The implanted pump is programmed by the healthcare team to deliver a continuous infusion, and the reservoir must be refilled at regular intervals (typically every 1–6 months depending on the dose). Patients using intrathecal baclofen must attend all scheduled refill appointments, as reservoir depletion leads to abrupt withdrawal, which can be life-threatening.

What Should You Know Before Taking Baclofen?

Contraindications

Baclofen must not be used if you have a known allergy (hypersensitivity) to baclofen or any of the other ingredients in the formulation. Additionally, intrathecal baclofen must not be given via any route other than the intrathecal (spinal) route, and intrathecal baclofen is contraindicated in patients with untreatable epilepsy. Oral baclofen should be used with extreme caution in patients with active peptic ulcers, as it may worsen this condition.

Warnings and Precautions

Before starting baclofen, it is essential to inform your healthcare provider about your complete medical history. Several conditions require special attention, dose adjustment, or enhanced monitoring:

• Epilepsy: Baclofen may lower the seizure threshold. In patients with epilepsy, anti-epileptic medication should not be reduced or withdrawn during baclofen therapy, and seizure activity should be closely monitored. Intrathecal baclofen is contraindicated in patients with untreatable epilepsy.
• Kidney disease: Baclofen is primarily excreted by the kidneys. Patients with impaired renal function may accumulate the drug, increasing the risk of toxicity. Dose reduction is typically necessary, and renal function should be monitored regularly.
• Liver disease: Although baclofen undergoes minimal hepatic metabolism, liver function should be monitored periodically, particularly during long-term treatment.
• Respiratory conditions: Baclofen can depress respiratory function, particularly at higher doses or when combined with other CNS depressants. Patients with chronic obstructive pulmonary disease (COPD), neuromuscular respiratory weakness, or other conditions affecting breathing require careful monitoring, especially during the initial dosing phase of intrathecal baclofen.
• Psychiatric conditions: Baclofen should be used cautiously in patients with psychotic disorders, schizophrenia, depression, or confusional states, as it can exacerbate these conditions. Hallucinations, paranoia, and mood disturbances have been reported.
• Parkinson's disease: Baclofen may worsen symptoms in patients with Parkinson's disease and should be used with caution in this population.
• Cerebrovascular insufficiency: Patients with inadequate blood circulation to the brain should be monitored closely.
• Peptic ulcer disease: Baclofen should be administered with caution in patients with a history of peptic ulcers.
• Diabetes: Blood glucose levels should be monitored, as baclofen may affect glucose metabolism.
• Autonomic dysreflexia: Patients with spinal cord injuries above T6 may experience autonomic dysreflexia (sudden dangerous blood pressure increases). Changes in baclofen therapy can trigger or alter this response.

Scoliosis: Scoliosis (lateral curvature of the spine) has been reported in association with long-term baclofen use, particularly in children receiving intrathecal baclofen. Patients should be monitored for changes in spinal alignment, especially during growth periods.

Tolerance: Some patients may develop tolerance to baclofen during long-term treatment, meaning the medication becomes less effective over time. If tolerance develops, the doctor may recommend a temporary treatment interruption (drug holiday) before resuming therapy. Intrathecal baclofen dose holidays should only be conducted in a hospital setting with careful monitoring.

Pregnancy and Breastfeeding

Baclofen should only be used during pregnancy when clearly necessary and the expected benefit to the mother outweighs the potential risk to the fetus. There is limited clinical experience with baclofen use during pregnancy. Animal studies have shown some evidence of developmental effects at high doses, but data in humans is insufficient to determine the full risk profile. Women of childbearing potential should discuss family planning with their healthcare provider before starting baclofen.

Baclofen passes into breast milk, although the levels are expected to be low following intrathecal administration. Oral baclofen may result in higher levels in breast milk. The decision to breastfeed during baclofen treatment should be made in consultation with the treating physician, weighing the benefits of breastfeeding against the potential risks to the infant. If baclofen is deemed necessary, monitoring the infant for signs of sedation, poor feeding, or reduced muscle tone is recommended.

Driving and Operating Machinery

Baclofen can significantly impair the ability to drive or operate machinery. Common effects that may affect performance include drowsiness, dizziness, visual disturbances, impaired coordination, and hallucinations. Patients should not drive or perform activities requiring full alertness until they know how baclofen affects them. The sedative effects are more pronounced at the start of treatment, after dose increases, and when baclofen is combined with other CNS depressants or alcohol.

How Does Baclofen Interact with Other Drugs?

Baclofen has clinically significant interactions with several categories of medications. Because baclofen acts as a central nervous system depressant, its effects are additive with other drugs that depress CNS function. It is critical to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter products, and herbal supplements.

Major Interactions

Minor Interactions

• Other muscle relaxants: When transitioning from oral muscle relaxants (such as tizanidine or dantrolene) to baclofen, the previous medication should be tapered gradually to avoid additive effects and withdrawal complications.
• Sedating antihistamines: Antihistamines that cause drowsiness (such as diphenhydramine or chlorphenamine) can increase the sedative effects of baclofen.
• Sleep aids: Medications used for insomnia (such as zolpidem or zopiclone) combined with baclofen increase the risk of excessive sedation.
• Lithium: Concurrent use with lithium has been associated with increased hyperkinetic symptoms in some case reports. Monitoring is advised.

Intrathecal drug interactions: Administration of other medications directly into the spinal canal is generally not recommended during intrathecal baclofen therapy, as the interaction profile for co-administered intrathecal drugs has not been well characterized. Any decision to use intrathecal co-medications should be made by a specialist experienced in intrathecal therapy.

What Is the Correct Dosage of Baclofen?

Baclofen dosing is highly individualized and depends on the formulation (oral or intrathecal), the patient's age, the severity of spasticity, and the response to treatment. The fundamental principle of baclofen dosing is to start low and increase slowly (gradual titration), allowing the body to adjust and minimizing the risk of side effects. All dose changes should be made under medical supervision.

Adults — Oral Baclofen

Adults — Intrathecal Baclofen

Children

Elderly Patients

Elderly patients (over 65 years) may be more sensitive to baclofen's side effects, particularly sedation, confusion, and falls. Although standard doses may be used if kidney and liver function are normal, dose titration should be particularly slow and cautious. Some elderly patients achieve adequate spasticity control at lower doses. Close monitoring for side effects, especially cognitive changes and orthostatic hypotension (blood pressure drop upon standing), is recommended.

Patients with Kidney Impairment

Since baclofen is primarily excreted through the kidneys, patients with impaired renal function require dose reduction. The starting dose should be lower, and dose increases should be made more slowly and cautiously. Regular monitoring of kidney function and clinical response is essential. In patients on hemodialysis, an additional dose may be needed after each session, as hemodialysis can remove baclofen from the blood.

Missed Dose

If you miss a dose of oral baclofen, take it as soon as you remember unless it is nearly time for your next scheduled dose. In that case, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you frequently forget doses, consider using a pill organizer or setting reminders. For intrathecal baclofen, the pump delivers medication continuously, so missed doses are not a concern — but missed pump refill appointments are a medical emergency risk.

Overdose

Signs and symptoms of baclofen overdose include:

• Unusual or profound muscle weakness
• Extreme drowsiness, confusion, or loss of consciousness
• Dizziness and unsteadiness
• Excessive salivation
• Abnormally low body temperature (hypothermia)
• Nausea and vomiting
• Respiratory depression or respiratory arrest
• Seizures
• Cardiac conduction abnormalities

For intrathecal baclofen, overdose can occur due to pump malfunction, programming errors, or accidental bolus administration. Intrathecal overdose symptoms may develop rapidly and require emergency medical intervention, potentially including temporary removal of cerebrospinal fluid containing baclofen. Hospital admission and intensive care monitoring are typically required for significant overdoses.

What Are the Side Effects of Baclofen?

Like all medications, baclofen can cause side effects, although not everyone experiences them. Side effects are more common at the beginning of treatment, during dose increases, or when doses are too high relative to individual tolerance. Many side effects diminish as the body adjusts to the medication. The following side effects apply primarily to intrathecal baclofen, though oral baclofen shares many of the same effects at corresponding frequency levels.

Pump and delivery system complications: Intrathecal baclofen therapy carries additional risks related to the implanted pump and catheter system. These include infections at the pump site, inflammation of the spinal membranes (meningitis), and inflammation at the catheter tip. Patients should report any signs of infection (redness, swelling, warmth, or discharge around the pump site), fever, severe headache, or new neurological symptoms to their healthcare team immediately.

How Should You Store Baclofen?

Proper storage of baclofen is essential to maintain the medication's effectiveness and safety throughout its shelf life. Follow these storage guidelines:

• Oral tablets: Store at or below 25°C (77°F) in the original packaging, protected from light and moisture. Keep in a dry place away from bathrooms and kitchens where humidity may be high.
• Intrathecal solution: Store at or below 30°C (86°F). Do not freeze. After opening, the solution should be used immediately. Intrathecal baclofen is restricted to hospital/clinic use and is handled by healthcare professionals.
• Child safety: Store baclofen out of the sight and reach of children. Consider using a locked medicine cabinet, as baclofen overdose can be dangerous.
• Expiration date: Do not use baclofen after the expiration date printed on the package. The expiration date refers to the last day of the stated month.
• Visual inspection: For intrathecal solution, do not use if the solution is not clear or if it contains visible particles.

Do not dispose of unused medication by flushing it down the toilet or placing it in household waste. Return unused or expired baclofen to your pharmacy for safe disposal. Many pharmacies and communities offer medication take-back programs. Proper disposal helps protect the environment and prevents accidental ingestion.

What Does Baclofen Contain?

Each baclofen product contains baclofen as its sole active ingredient. The inactive ingredients (excipients) vary by formulation and manufacturer:

Oral tablets (10 mg, 25 mg): Common excipients include microcrystalline cellulose, lactose monohydrate, maize starch (corn starch), pregelatinized starch, colloidal anhydrous silica, and magnesium stearate. Patients with lactose intolerance should be aware that most oral baclofen formulations contain lactose.

Intrathecal solution (0.05 mg/ml, 0.5 mg/ml, 1 mg/ml, 2 mg/ml): The intrathecal formulation contains baclofen dissolved in sodium chloride (saline) and water for injections. It is a clear, colorless solution presented in prefilled syringes or vials. The solution contains less than 1 mmol of sodium (23 mg) per maximum daily dose and is considered essentially sodium-free.

Packaging: Intrathecal baclofen 0.05 mg/ml is available as a 1 ml prefilled syringe (used for test doses). The 0.5 mg/ml, 1 mg/ml, and 2 mg/ml concentrations are available as 20 ml prefilled syringes or 20 ml vials (used for pump filling). Oral tablets are typically supplied in blister packs or bottles.