Skeletal muscle relaxants can cause various side effects. Some patients experience blurred vision, clumsiness or unsteadiness. Other side effects associated with muscle relaxants include:

• Dizziness
• Drowsiness
• Fainting
• Lack of alertness
• Lightheadedness

Some side effects may be more serious, and include abdominal pain, breathing difficulties, blood in urine or stool, sore throat and fever. The skeletal muscle relaxant quinine sulfate has been associated with rare but potentially life-threatening heart problems. Patients who take these medications are advised to promptly report any significant side effects to a physician.

Because of the tendency for skeletal muscle relaxants to cause drowsiness, people are urged to avoid taking these drugs before certain activities (e.g., driving, using machinery) unless they know how they are likely to be affected.