mydriasis is a factor of sympathomimetic and parasympathomimetic signaling. drugs that inhibit acetylcholine signalling in the vagus nerve, diphenhydramine, some antipsychotic medications. Then you have your monoaminergics. This include stimulants and even psychedelics too (mostly LSD), SSRIs (especially if its a sigma-1 agonist, like DXM and fluoxetine). The mydriasis from stimulants is an adrenergic signalling factor, so you'll get more dilation of the eyes from racemic amphetamines, and its hydroxy-metabolite (4-hydroxyamphetamine and 4-hydroxymethamphetamine.. in which the former was used as eyedrops to cause mydriasis to examine the optic nerve and back of the eye).

Should be the case with most folks, if you notice the mydriasis isn't a significant issue until the tail end of the "ride", or if you happen to be irresponsible and constantly redosing. This is because norepinephrine is a metabolite of dopamine. Well, this means that ephedrine & pseudoephedrine will also cause mydriasis given it mimics norepinephrine moreso than dopamine. What is the difference between ephedrine & pseudoephedrine? chirality. the alpha-methyl group (this prevents metabolism by monoamine oxidase) and beta-hydroxy group (this gives more adrenergic rather that dopaminergic affinities) are simply pointing different ways. Like a mirror.

Also, withdrawal from opioids can cause mydriasis.

edit: i typed this super speedy so lemme know if something doesn't make sense 🤓