I'd be interested in hearing discussion about the study, and whether your experiences seem to match the findings (for those of you who have tried both forms of the drug).

The full text is available here. It is a double-blind and placebo-controlled study from researchers in Switzerland and was published in late 2017.

In contrast to our hypothesis, no differences were found in the peak plasma concentrations of amphetamine and the associated subjective and cardiovascular peak effects between lisdexamfetamine and D-amphetamine. Increases in the plasma concentrations of amphetamine occurred an average of 0.6 h later and reached peak levels 1.1 h later after lisdexamfetamine administration compared with D-amphetamine administration, but the amphetamine concentration-time and drug effect-time curves were otherwise comparable between treatments. Thus, the pharmacokinetics and pharmacodynamics of a high dose of the newly marketed medication lisdexamfetamine were practically identical to an equimolar dose of the classic immediate-release D-amphetamine administered 1 h later.

(emphasis added)

Plasma concentration (graphs)

Subjective effects (graphs)

Do you think the differences some people seem to experience between these medications are down to the placebo effect, or some other factor the study did not address?

Cheers :)

edit: short term tolerance (i.e. during the day) based on the magnitude and duration of ascending concentrations might be the key. See my comments below.