I can’t imagine it being unsafe (assuming the drug itself doesn’t do damage) since the restriction would let less light in. It’s not like forcibly dilating the pupil which could let in more light than the eye could handle. It could make things appear too dark while it’s happening though.

Wait, is this why when I'm having trouble seeing something small, it becomes easier when I get way more light on it?

I just assumed more photons results in a stronger signal to my rods and cones. But maybe it's making my eye shrink the aperture instead (or both).

Oh it's worse than that just pupil shrinking in dark. Basically, cone cells see color and detail but need more light, rods see in low light but mostly serve peripheral vision. So your vision system is just wholly optimized to only doing detail work in fairly bright light; nighttime is for predator evasion.

Another way to look at that: We likely evolved decent color vision to identify edible fruits. That wasn't doable with vision in the dark (and we opted out of the olfactory tech tree), so now your accurate-vision tasks are optimized for daylight.