Why do some pills require a prescription, but not sudafed?

because it is considered safe when used as recommended.

It has bee placed behind the counter to discourage meth cookers.

@DrBill aren’t prescription pills considered safe when used as recommended?

@marinelife look up smurfing. Dealers give dopers a rock in exchange for them going in and buying the sudafed.

There is a reason why some medication requires a prescription from a doctor. Usually the reasons are that the medication has a high potential for abuse or overdose. It may be in short supply, or simply that it is so specific in it’s use that it is only practical to be given to a select few patients.
Sudafed has now been placed behind counters and that way the medicine can be monitored for sales..