How exactly does cold and flu medicine work inside the body? when it enters the bloodstream, does it begin fighting the bacteria causing symptoms?

Treats symptoms: In general, Cough and cold medicine do not attack bacteria. Most of the time they provide symptomatic relief. For example, Ibuprofen or acetaminophen help with body aches and fever, pseudoephedrine helps with congestion, guaifenesin help loosen up mucus secretions. Antibiotics and antivirals typically attack infectious organisms. Ultimately it's your body that gets rid of the infection.