Why might a generic brand from a different manufacturer feel less effective, even at the same dose?

So, this is quite a complicated one, without dissapearing too far into psychopharmacology....ADHD is thought to be a deficit in dopamine production.ADHD medication ,through various means, increases either the level of dopamine or the availibility of existing dopamine. Some formulations of medication do that better and most of the time we are not 100% sure why. Different manufacturers may use different inactive ingredients like, tablet coatings, capsule materials, or manufacturing processes. For modified-release medications, there may also be different technologies used to control how the medication is released throughout the day. Although these products must meet regulatory standards, some people report that they notice differences in how quickly the medication starts working, how long it lasts, or how smooth the effects feel. Everyone responds to medication slightly differently, so while many people can switch between manufacturers without noticing any change, others find that one version suits them better than another.