Why do you need a prescription for large amounts of codeine

I broke my foot a while ago, i was using panadine extra (paracetamol 500mg, codeine 16mg per tablet). But it didnt help with the pain much. I told the doctor and he said to get panadine forte (paracetamol 500mg, codiene 30mg per tablet). He said you dont need a prescription but when i got to the pharmacy, they wouldnt give it to me without one. I went back to the doctor and got a prescription and went to get the panadine forte, and the pharmacists were all unsure about giving it to me, they were all like "have you had this before?" and i was like "yes" (i'd had it a few years back). and they were like "are you SURE" and i was like "YES". So now im sitting at home with my panadine forte wondering why it sounded like it was so bad?

Because of withdrawal and dependence that people can develop from it.
As with other opiate-based pain killers, chronic use of codeine can cause physical dependence. When physical dependence has developed, withdrawal symptoms may occur if a person suddenly stops the medication.