Not sure about, in regards to meds one way or the other (as I don't take any due to sensitivities, or the negatives outweighing the benefit).
But, I can say that there's definitely something major going on for me, in regards to whether or not I'm stimulated through interest and/or enjoyment from, or in, what I'm doing.
If a topic is dull and/or not of real interest, or engaging to me, it is likely that I won't be able to focus deeply upon it for long.
Definitely when it comes to reading and/or doing any repetitive process, it puts me into a secondary day dreaming state and/or nodding off state -microsleeps-; even when it comes to chit chatting with people socially (am not big on socializing 'in groups' because it can be so monotonous), I find it difficult to concentrate enough to even participate.
The same sort of 'staying stimulated through interest/enjoyment' goes for activities, physically, if I'm not enjoying it then it seems to drag out over a short period of time and I'll become weak as well as tired; versus if I'm enjoying the activity, it will fly by and I'll manage it much more comfortably for longer than I expect (to be able to have managed it), often.
Seems to be a double edged blade, at times.