What is a Red round pill with the letter c on it?

This is an international website - if you resubmit this question with a country / state / province indicated where the pill was obtained, your odds of getting a "good answer" are much higher. Similarly, there are many differently sized and tinted red pills out there. Just sayin'.

You may wish to use search engines and look for a hardbound reference manual titled (in the USA) "The Physician's Desk Reference" ( commonly known as the PDR), which has a section of photographs of many pharmaceuticals. And as always don't ever, ever let anonymous strangers guide you about potentially life-and-death matters such as medicine.