Cyclobenzaprine HCL 15 mg ER is an extended-release muscle relaxant used to ease muscle spasms, tension, and discomfort caused by acute injuries or strain. It works by calming nerve activity so your muscles can relax throughout the day. The extended-release formula provides steady relief, which helps you stay comfortable without frequent dosing. Many people use it to manage stiffness, improve mobility, and reduce pain during daily activities. It is usually taken once daily and is most effective when combined with rest, gentle stretching, and physical therapy. While it offers strong relief, it may cause drowsiness, dry mouth, or dizziness in some people, so it’s important to follow your doctor’s guidance.