Is it possible to become addicted to enchanted items or spells? For example if a spell made a character smarter or a ring made a character stronger could they become addicted to using it? If so what would be the negative side affects?
Awesome question.
There are no hard and fast rules for this in any game I'm familiar with, so its really up to the player and their DM(if its that kind of game) to decide how they
want to proceed.
The side effect should really depend heavily on the item itself and how its being used. In the example of a ring of strength, there are two possible effects. The first is that the owner wears the ring all the time, but never does any strenuous activity. This causes his body to rely on the magic of the ring for physical tasks, and the natural muscle slowly decays away. Its the same principle as if you spent a year on the moon. Because your body doesn't have to fight so hard against gravity, your muscles would become weak, and when you came back down to earth, you would have a very hard time standing up.
In this scenario, it would only progress so far. We assume that the person performed the same daily tasks day after day before obtaining the ring as he did after. In that case, body would let its own muscle decay to the point where the person would have to use the ring in order to have the same amount of strength now that he had before he got the ring.
However, if he increased the amount of daily tasks or excersice he does in an amount proportionate to the amount of increase in strength provided by the ring, he would see no side effects.
These are a very natural array of effects. The same thing would happen if you suddenly found yourself on the moon.
There could also be side effects that come from the constant influx of magic to the body. Perhaps the person develops an immunity to the type of magic, the same way his immune system will develop an immunity to chicken pox after having it. Perhaps the ring stops working on him after awhile. Or perhaps all magic stops working on him after awhile.
Or there could be the other method of the body adapting to the constant influx of magic. It could learn to use that same magic in new and interesting ways. Perhaps you learn how to cast a Strength enhancing spell on yourself, even when not wearing the ring. Perhaps you learn how to cast the spell on others while you are wearing the ring.