Low back pain or lumbago is a common musculoskeletal disorder affecting 40% of people worldwide at some point in their lives. Low back pain (often abbreviated as LBP) may be classified by duration as acute (generally pain lasting less than six weeks), sub-chronic (six to 12 weeks), or chronic (more than 12 weeks). The condition may be further classified by the underlying cause as either mechanical, non-mechanical, or referred pain. For most episodes of low back pain, a specific underlying cause is never identified or even sought, and the pain is attributed generally to mechanical problems such as muscle strain or joint sprain. The management of low back pain typically includes the use of medications for the duration that they are beneficial, and expert groups recommend the use of acetaminophen as the first thing to try. With conservative measures, the symptoms of low back pain typically show improvement within a few weeks from onset.