Prescribed medication is by a doctor, dentist or other authorized person, in order to treat or manage a medical condition. Pain medication are much more stronger, and used to treat more serious pain from surgery, injury or disease. Some prescribed pain medications, affects the CNS Central Nervous System, and can be addictive hence they are a prescription drug.
Over The Counter OTC's medications can bought with out a prescription, often to treat minor ailments or conditions.
Such as Panadol and Aspirin used for pain relief and Cough and cold treatments, they don't have sufficient quantities of addictive ingredients if at any.
However many people don't realize that OTC or complementary medication, can interact with prescribed medication or may even cause unwanted side affects, such as pseudoephedrine that is found in some cough & cold preparations and should not be used by those with heart murmurs. Therefor doctors need to know if we are taking OTC or Complementary medication.
Not sure if this is going to help, but I hoped it helped a little