As prescribed, it's at a much lower dosage. Adderall is tuned in 10mg increments, and meth is sold by the gram. Moreover, you absolutely can get addicted to and have serious health problems from prescribed medication -- it's a balance of risk versus reward. A handful of people prescribed stimulants have suffered sudden cardiac death.

The main difference here is modality of use -- taking something, once per day, in controlled doses, is very very different from taking something until you feel good. With a prescription, you also have a steady supply and no need to commit crimes to keep up your supply. So the societal problems from drug abuse, like overdose, increased criminality, and breakdown of relations don't happen with prescription drugs to the same extent, even if it's the same substance. Look at when the opoid crisis became a crisis -- it was when cheap, easy opioids stopped being available.