meth and amphetamine are quite similar, most people can't tell the difference between them if they just take it orally... but there is also differences between types, adderall contains a bit of L amphetamine and much of the european amphetamine supply is 50/50 D,L and this has an impact on the effect also, you may also be familiar with the name "dexedrine" or "dexies" these are more common in Australia and are pure D amphetamine
i was on dexies for a while, but i found they made me too nervous and slowed me down too much, whereas european paste tends to make me a bit overly horny lol
anyway, point was just that amphetamine especially blends of D and L can have a paradoxical effect, and it especially tends to happen with people who are normally hyperactive or impulsive