Question: what is the best over the counter medicine for lower back pain?
Answer: Ibuprofen (such as Advil or Motrin), available over-the-counter, is an excellent medication for the short-term treatment of low back pain. ... 
Acetaminophen (such as Tylenol) is also effective in relieving pain.
Topical agents such as "deep heating rubs" have not been shown to be effective.