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.

Adderall is amphetamine salts not methamphetamine. While methamphetamine can be prescribed for ADHD/occasionally weight loss, it's pretty rare in the US. That said, the mechanism of action is very similar

Methamphetamine is an effective ADHD medication (brand name Desoxyn). Adderall contains amphetamine (not methamphetamine). Although as far as how it compares to amphetamine, I would say they are nearly identical on a dose equivalent basis.

Here is an interesting look at the differences between ADHD medications: https://astralcodexten.substack.com/p/know-your-amphetamines

They're basically the same thing. Difference is ADHD meds are 5-10mg Meth, or similar drug at a lowish dose, and orally. But you can take meth a low dose and achieve the same effect.

Taking more doesn't help your performance, it makes it worse, and you get way more side effects, especially mental side effects. These build up with time.