In the US, generics only have to be within 10% of equivalent blood concentrations. Plus, the inactive ingredients and the time-release mechanism can be totally different. The first real issue with this in ADHD stimulant medications was with Concerta. The FDA approved generics that didn’t work at all the same — at least some not even having the same time-release mechanism that is unique to Concerta and a great part of it’s efficacy. With many complaints, the FDA actually revoked the equivalency status of 2-3 of the generics. Now there’s another new generic approved and I hear it’s even worse than the ones originally changed.
I have heard many reports of Adderall generics not being equivalent either.
What we did during the Concerta “crisis” (it was a crisis to us!), was the doctor wrote “brand medically necessary” on the prescription so the insurance would pay for brand.
Here’s a prior discussion on Adderall generics as well: https://www.additudemag.com/forums/topic/genetic-adderral/
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism