It should be noted that TEVA manufactures both Generic and Brand forms of Adderall IR, having acquired the rights when they acquired BARR, which itself bought the rights from Shire PLC (now Takeda).
The brand and generic forms were actually pretty similar for a number of years, following the acquisition; but the generic has in my opinion degraded over the course of the last two years.
Why do I think this? Because I was taking TEVA generic Adderall in 2014, then switched to the brand form, and took that until late 2018, when I switched back to the generic. Although I don’t recall any longer what switching back to generic was like, I do remember that switching to the brand version in 2014 didn’t seem to make much difference. At the same time, I can also say that for over a year now, I have consistently felt a worsening in the effectiveness of the generic. By now (11/2011) the generic made by TEVA does little to keep me awake, causes various physical side effects, and also wears off more quickly. I remember waking up more easily in the morning while I was taking the brand version, because I could still feel the effect from the previous day. By comparison, the generic at this point no longer keeps me awake at all — an odd thing, considering this is supposed to be an amphetamine.