The goal of this clinical trial is to learn if a modification to metaxalone 640 mg can reduce low back and leg pain. The participants will be 18 to 80 years old, healthy with newly occurring back or leg pain. The main question aims to compare a group taking active treatment and a group taking a look-alike substance containing no active treatment. All participants will answer questions on Day 1, before treatment, and on 7-day after treatment, about:

• Amount and quality of pain
• Interference with physical activity
• Interference with sleep

Double-blind, randomized, placebo-controlled, multi-center study of metaxalone 640 mg plus standard of care for patients with acute lumbo sacral musculoskeletal conditions with spinal stenosis and sciatica. Participants will be randomized 1:1. Following the initial pilot-study a second study will randomize a larger population of patients with appropriate power.

Inclusion Criteria:

• No clinically significant conditions impacting quality or quantity of pain
• Baseline Numeric Pain Scale ≥ 6
• Capable of answering text or email survey reminders
• Low back pain with or without sciatica

Exclusion Criteria:

• Current use of other skeletal relaxants
• Current use of other pain relievers
• Current use of cimetidine or monoamine oxidase inhibitors