If you have never taken ADHD stimulants before then you might experience a little bit of euphoria the first few days of stimulant therapy, due to lack of tolerance, but I doubt it would be an impairment to driving.

Source: I've been taking methamphetamine (prescribed) for ADHD for quite some time. I experienced a little euphoria the first week when I initially started treatment on amphetamines but it was nothing even close to what I would consider impairment.