here is a very old one, but oral not i.v.: https://pubmed.ncbi.nlm.nih.gov/4900434/
5mg/10mg amphetamine sulphate vs 300mg and 600mg of caffeine (all oral). The study scales ended up being skewed because one subject had paradoxical response and felt relaxed instead on amphetamines, lol.
If you have access to the full text, check out page 89: fig5 and fig6.
Volkow's lecture may have referenced multiple studies, I've heard that in the context of her lecture on various findings on psychostimulants. amphetamines and cocaine have been fairly repeatedly shown fairly consistent substitutes, so it may have been a study on amp vs caffeine.
She just loves to study and talk about cocaine for some reason, has literally a hundred+ papers on it.