I think part of the stigma is that ADHD is very hard to diagnose. And even people without ADHD can yield benefits from taking stimulants. For years, it was perpetuated that these drugs calm kids with ADHD down, but have a different effect on health people. Actually, the drugs do exactly the same thing in people whether they are hyperactive, have problems paying attention, or are healthy. They improve focus by increasing the levels of the neurotransmitters norepinephrine and dopamine in the prefrontal cortex, the front part of the brain that regulates attention and behavior. Basically, light that up and everything else gets controlled. But your heart still races.

To get a little technical, here's an article from Neuropsychopharmacology:

"For years, it was assumed that stimulants had paradoxical calming effects in ADHD patients, whereas stimulating 'normal' individuals and producing locomotor activation in rats. It is now known that low doses of stimulants focus attention and improve executive function in both normal and ADHD subjects. Furthermore, the seminal work of Kuczenski and Segal showed that low, oral doses of methylphenidate reduce locomotor activity in rats as well."

Often you hear that if stimulants like Ritalin, Vyvanse, or Adderall help people stay calm, that means that they must have ADHD. This isn't true. These drugs will help anyone focus and pay attention. Giving stimulants to a kid with ADHD is more like giving a child with a learning disability more time on a test -- and advantage that might help anybody, but helps that child more -- than fixing his brain.