Can you heal a cold/flu without medicine?

Sometimes.: It's difficult to generalize since there is a whole spectrum of severity and multiple possible causes of colds and flu. However, in general, it's helpful to keep oneself very well hydrated and hot liquids increase blood flow to the areas in contact with the liquid. Chicken soup is helpful; it has lots of protein. Rest is important. Tylenol (acetaminophen) can help with fever and pain.

Yes: The vast majority of colds/flu heal with no medicine.