What pill is white oblong has P500 on one side and blank on other?

Acetaminophen 500mg.

Acetaminophen is used in the treatment of pain; muscle pain; sciatica; fever; neck pain (and more), and belongs to the drug class miscellaneous analgesics. Risk cannot be ruled out during pregnancy. Acetaminophen 500mg is not a controlled substance under the Controlled Substance Act (CSA).

https://www.drugs.com/acetaminophen.html