Exploratory Efficacy Study of Guaifenesin in Upper Back Pain

Inclusion Criteria: * Paticipant presents with a new episode of acute upper back/neck/shoulder pain and muscle spasm that: 1. is at least 30 days from previous episode. 2. has an onset occurred within 48 hours of Visit 1. 3. has symptoms consistent with a clinical diagnosis as per the physical examination at Visit 1. 4. has a subject-rated muscle spasm score and a pain score of at least 40 out of 100 on a 100mm VAS. * Paticipant has a normal neurological examination. Exclusion Criteria: * Medical history: a) Paticipant has a known or suspected intolerance or hypersensitivity to guaifenesin or methocarbamol (or closely related compounds) or any of their stated ingredients. b) Paticipant has history of upper back pain with active hypersensitive spots - trigger point in the muscles of upper back/neck/shoulder/maxillofacial regions. c) Paticipant has a current or recent history of liver and/or kidney disease, neck/back/shoulder injuries, spinal disc disease, myocardial infarction (\<12 months from Visit 1) and osteoporosis. d) Subjects have history of other chronic pain e.g. headache, osteoarthritis, arthritis, lower back pain etc. * Medications: a) Paticipant has used a muscle relaxant or narcotic within 2 weeks of Visit 1. b) Paticipant has used monoamine oxidase inhibitors or selegiline within 2 weeks of Visit 1 c) Currently using tricyclic antidepressants, lithium, anticoagulants, or tramadol. * Paticipant is involved in a workers compensation case. * Paticipant is unlikely to refrain from using analgesics, NSAIDs, and other muscle relaxants for the duration of the study, with the exception of cardioprotective doses of aspirin (i.e., ≤ 325 mg/day). * Paticipant is unlikely to refrain from physical therapy, massage therapy, acupuncture, heat treatment, spas, etc for the duration of the study.