vitamins is harmfull if more used  

that's true. every intake of drugs or vitamins has an effect.. especially to one's liver..

Is it the drug addiction if too much or excessive intake of vitamins.

Thats with everything though, it is able to actually drink yourself to death. (Water..)

yes if vitamins r taken in our doase. then it will be harmful.
every think which we take in excess then it will be harmful.

It depends on what type of vitamins are you taking in. Like for example, comparing Vitamin B Complex with Vitamin A (especially the Beta-Carotene), there is harmful effect to the body if you take Vit. B Complex in excess to those prescribed by the physician. On the other hand, taking excess of Vitamin A (Beta-carotene, not the Retinol Acetate variant), excessive amount of Beta-Carotene is safe to the body. But take caution of Vitamin A Beta-Carotene, because excessive amount of that type of Vit. A can be harmful to the body! If you want to know the difference between the two, both are Vitamin A, but the difference is, Beta-Carotene is plant-based substance while Retinol Acetate is a type of Vitamin A extracted from animal source. Generally speaking, plant-based or vitamins extracted from plants are safer than vitamins extracted from animals.

Well true too much of vitamins can causes liver problem and others.