I thought diet pills were not addictive so why is meth?

Depends on the pill: Some diet pills can be quite addictive, and methamphetamine certainly has that potential. The essence of addiction is needing more and more of a substance to achieve the desired outcome such as weight loss. Any time you find yourself needing something more frequently or in greater amounts or to avoid some sort of side effect from "coming down, " think addiction.

See below: Typically, the addictive stimulants have a predominance of Dopamine stimulation. While diet pills may have some Dopamine stimulation, their primary effect is to stimulate norepinephrine which is not an addictive effect.