No, Baclofen and Flexeril (Cyclobenzaprine) Are Not the Same Medication
Baclofen and cyclobenzaprine are distinct medications with different mechanisms of action, indications, and safety profiles. While both are classified as muscle relaxants, they work through entirely different pathways and should not be considered interchangeable.
Key Differences
Mechanism of Action
- Baclofen is a GABA-B (gamma-aminobutyric acid type B) receptor agonist that works primarily at the spinal level to reduce spasticity 1, 2, 3
- Cyclobenzaprine is structurally related to amitriptyline and acts as a 5-HT2 receptor antagonist with central anticholinergic activity 2, 4
Primary Indications
- Baclofen is specifically used for spasticity resulting from central nervous system injury, demyelinating conditions, and other neuromuscular disorders 2, 5
- Cyclobenzaprine is approved for acute musculoskeletal pain but has no evidence of efficacy in chronic pain and does not directly relax skeletal muscle 1
Critical Safety Considerations
Baclofen Carries Higher Risks
Recent high-quality evidence demonstrates that baclofen poses significantly greater safety concerns compared to cyclobenzaprine:
- Encephalopathy risk: Baclofen carries 2.29 times higher risk at 30 days and 1.94 times higher risk through one year compared to cyclobenzaprine 6
- Fall risk: Baclofen shows comparable fall risk to cyclobenzaprine in older adults 7
- Opioid overdose: When combined with opioids, baclofen has 2.52 times higher risk of overdose compared to cyclobenzaprine 8
- Postoperative delirium: Baclofen/cyclobenzaprine use increases delirium risk 2-fold after lumbar fusion in older adults 9
- Injury risk: Baclofen demonstrates 69% greater risk of serious injury (fractures, falls, brain injury) compared to cyclobenzaprine in older adults 10
Withdrawal Concerns
Baclofen requires careful tapering when discontinuing due to risk of severe withdrawal symptoms including psychiatric disturbances, delirium, agitation, and autonomic instability, typically emerging 1-4 days after abrupt discontinuation 2, 11. Cyclobenzaprine withdrawal causes only mild, non-life-threatening symptoms (malaise, nausea, headache) 4.
Clinical Implications
When to Use Each Medication
- Use baclofen only for true spasticity from CNS injury or demyelinating disease, not for routine musculoskeletal pain 1, 2, 5
- Cyclobenzaprine may be considered for acute musculoskeletal pain (not chronic), though guidelines note these drugs "do not directly relax skeletal muscle" 1
Avoid in Older Adults
Neither medication is favored for chronic pain in older adults due to adverse effect profiles 1. The 2023 Beers Criteria recommends avoiding skeletal muscle relaxants for musculoskeletal complaints in older adults, and recent evidence suggests baclofen should be included in this recommendation 10.
Common Pitfall
Do not prescribe these medications interchangeably or assume they have equivalent safety profiles. Baclofen's significantly higher risk of encephalopathy, falls when combined with opioids, and severe withdrawal syndrome distinguishes it as a higher-risk agent requiring more careful patient selection and monitoring 10, 7, 6, 8.