Yes you definitely need a prescription for some drugs, I dont know if there is a list anywhere detailing those only available on prescription, or alternatively, those available over the counter. For specific drugs, a chemist would be able to advise. I have just had an operation here in Fethiye and was given a prescription for anti coagulant injections,the doctor said I needed them for 30 days. The chemist informed me that only 10 days supply can be given on one prescription at the start, so I will need another prescription from the doctor, but then can have the other 20 days in one go as I will have already been taking this drug. So obviously guidelines, but difficult - why am I not surprised!
I think if I was on any sort of medication,I would ask a chemist if this is available over the counter or if a prescription is needed. Obviously the cost then would rise as the doctor would have to be paid.