This is a little round pill, white, with MYLAN embossed on one side and 377 on the other. Mylan 377 is 250 mg Naproxen (generic Naprosyn, or Aleve, or Midol), the smallest dosage of the medication manufactured by Mylan Pharmaceuticals. Being an NSAID, Naproxen is used for the treatment of inflammation and as pain-killer. As only dosages of 220 mg or less (e.g., Aleve) are available over-the-counter, to get Mylan 377 pills you normally have to obtain a prescription.
Beware that Naproxen increases your risk of life-threatening heart or circulation problems, including heart attack or stroke. It can also increase your risk of serious effects on the stomach or intestines, including bleeding or perforation. Long-term usage of the medication can worsen its adverse effects.