Baclofen and Flexeril (cyclobenzaprine) are not the same medication. While both are classified as skeletal muscle relaxants, they belong to different drug categories, work through entirely different mechanisms in the body, and are prescribed for different conditions. Confusing them could matter, because one treats neurological spasticity while the other targets short-term muscle spasms from injuries or back pain.
Different Drug Categories
Skeletal muscle relaxants fall into two distinct groups: antispastic agents and antispasmodic agents. Baclofen is an antispastic drug, designed for neurological conditions like multiple sclerosis, cerebral palsy, and spinal cord injuries where the brain or spinal cord sends abnormal signals that keep muscles persistently tight. Flexeril is an antispasmodic, meant for acute musculoskeletal conditions like a pulled muscle, back strain, or neck pain from an injury.
This distinction matters practically. Baclofen lacks strong evidence for treating ordinary muscle pain from strains or injuries, and prescribing guidelines specifically recommend against using antispastic agents for those conditions. Likewise, Flexeril isn’t designed to manage the ongoing, neurologically driven muscle tightness seen in conditions like MS.
How Each Drug Works in the Body
Baclofen is a derivative of GABA, the brain’s primary calming chemical. It activates specific GABA receptors in the spinal cord and brain, amplifying the body’s natural inhibitory signals. This quiets the overactive nerve pathways responsible for spasticity. By increasing potassium flow out of nerve cells and reducing calcium entry, it suppresses the spinal reflexes that cause muscles to stay locked in a contracted state.
Cyclobenzaprine works through a completely different pathway. It is structurally almost identical to tricyclic antidepressants like amitriptyline and imipramine. The FDA label describes it as a “tricyclic amine salt,” and animal studies confirm it shares key properties with those antidepressants: it boosts norepinephrine activity, has strong anticholinergic effects (blocking a neurotransmitter involved in many body functions), and produces sedation. Rather than acting at the spinal cord level like baclofen, cyclobenzaprine is thought to reduce muscle spasm by acting within the brainstem. It is the most studied skeletal muscle relaxant in its class.
What Each Drug Treats
Baclofen is prescribed for spasticity caused by damage to the central nervous system. People with MS, spinal cord injuries, or cerebral palsy may take it long-term to manage the stiffness, involuntary muscle contractions, and pain that come with these conditions. In some cases, it can be delivered directly into the spinal fluid through an implanted pump when oral doses aren’t sufficient.
Flexeril is approved for short-term relief of muscle spasms tied to acute, painful musculoskeletal problems. Think of it as a temporary tool for something like a back injury or a muscle strain. The FDA is clear on duration: use should be limited to two or three weeks, because there’s no good evidence it works beyond that window, and the conditions it treats typically resolve on their own in that timeframe.
Side Effects Compared
Both drugs cause drowsiness, which is their most common side effect. But the reasons behind the sedation differ, and so do some of the other effects you might notice.
Baclofen’s sedation comes from its GABA activity, the same system targeted by drugs like alcohol and certain sleep aids. Other common side effects include dizziness, weakness, nausea, and confusion. At higher doses, baclofen can cause significant drowsiness or even reduced consciousness, particularly when combined with other drugs that depress the central nervous system.
Cyclobenzaprine’s side effects mirror what you’d expect from a tricyclic antidepressant. Dry mouth is very common because of its anticholinergic properties. Drowsiness, dizziness, and blurred vision are also typical. Because it shares so much pharmacology with tricyclic antidepressants, it carries a specific and serious interaction warning: it must not be taken with or within 14 days of MAO inhibitor medications. That combination has caused dangerously high fevers, seizures, and deaths.
Stopping Each Medication Safely
This is one of the most important practical differences between the two drugs. Baclofen requires careful, gradual dose reduction when it’s time to stop. Abruptly discontinuing baclofen can trigger a withdrawal syndrome with serious symptoms: restlessness, insomnia, confusion, hallucinations, seizures, high fever, and worsening spasticity. In severe cases, particularly at high doses, sudden withdrawal can mimic a life-threatening condition called neuroleptic malignant syndrome, with dangerous fluctuations in heart rate, blood pressure, and body temperature.
Flexeril, by contrast, is typically used for such a short period (two to three weeks) that withdrawal is far less of a concern. It can still cause some rebound effects if stopped after regular use, but it doesn’t carry the same risk profile as baclofen discontinuation.
Can They Be Substituted for Each Other?
No. Swapping one for the other would mean using a drug outside its intended purpose, with little evidence it would help and real potential for harm. If you have a back strain and are prescribed Flexeril, baclofen would not be an appropriate alternative. If you’re managing MS-related spasticity with baclofen, cyclobenzaprine is not designed for that type of muscle problem. The two drugs target fundamentally different types of muscle tightness through different mechanisms, and their treatment timelines (short-term versus long-term) reflect that difference.