Codeine and saliva. One side effect of Codeine is reduced saliva or dry mouth. Saliva helps dilute the effect of acid from bacteria that causes tooth decay. Any medication that leads to a dry mouth can lead to more tooth decay. There are over the counter products that can reduce the effect of dry mouth.
No, but be careful. Narcotics don't cause tooth decay directly. But, their prolonged effect on the body can, indirectly. Prolonged usage can lead to addiction and addiction effects can be like that of meth or other hard street drugs. Basically, the drugs make you stop caring about your mouth, much less anything else. That's when tooth decay sets in . . . When people stop taking care of their mouths.