Moreover, continued misuse of antibiotics can eventually lead to an infection that is resistant to antibiotic treatment - a dangerous and increasingly prevalent trend. Don't assume you need an antibiotic. The flu and common colds are viral infections. Antibiotics will not teat viral infections at all - they are only effective against bacterial infections. Never borrow someone else's medication.
Different antibiotics fight different bacteria.
What cured your friend's sore throat may not cure yours, particularly if your infection is not bacterial. Old medication also may have lost its effectiveness and could even be dangerous. Don't skip doses. Take your antibiotic exactly as directed. Taking it sporadically can hinder your recovery and can also lead to the growth of resistant bacteria.