Is the change of urine to brown when taking Naproxen and Tamiflu a cause for concern?

It is difficult to propose a specific diagnosis based on such a short description. The change in the color of urine to brown can have many causes. It can also be associated with dehydration, or specific foods (eg consumption of a large amount of rhubarb, beets). It can also be a sign of kidney disease. Hematuria is also mentioned as one of the side effects of Naproxen: https://www.gdziepolek.pl/produkty/51535/naproxen-500-hasco-tabletki/ulotka/82797 I encourage you to make an appointment with a primary care physician who will adjust the treatment according to your current clinical condition. If you are unable to get to your primary care doctor, the gdziepolek.pl service also allows you to obtain a teleconsultation with a doctor: https://www.gdziepolek.pl/telekonsultacja I enclose additional information that may be helpful: https://www.gdziepolek.pl/artykuly/czy-bac-sie-dzialan-niepozadanych-lekow https://www.gdziepolek.pl/artykuly/czy-przyjmowanie-kilku-lekow-jednoczesnie-jest-bezpieczne https://www.gdziepolek.pl/artykuly/czy-jak-i-kiedy-mozna-odstawic-leki