Metabolism plays a big role in determining the effective dose.
There are people who can take what are considered high therapeutic doses and feel very little effects because of the way their body metabolizes the chemical, which of course has nothing to do with whether they have ADHD or not.
For sure. I take adderall and have an incredibly high metabolism to the point of needing to add 1500 calories per day in protein shakes to stay at a healthy weigh.
7.5mg (15mg in half) is my usual dosage, but it's strong enough to fill me with the energy you'd expect someone on a high dosage to have. When I talk a full pill, it completely screws me over. Others can take 30mg and be completely fine.
There are people who can take what are considered high therapeutic doses and feel very little effects because of the way their body metabolizes the chemical, which of course has nothing to do with whether they have ADHD or not.