Cool concept. I finished it after a few attempts, I managed to clear the last level without taking the last pill ;)

A few remarks:
- you shouldn't restart the music each time you lose a life, it's a little annoying
- inertia of the character is not very interesting, the last level is really hard because of this and it's not fair
- sometimes I felt the space key was not working, maybe because I pressed just before taking a pill or just after falling off a cliff but anyway something is not good with the controls (check out 'coyote time' if you don't know what I mean)
- btw space is a terrible key for jumping because it's the leastprecise key!

update: I'm dump and didn't understand that the theme was literally 'limited number of spaces', I've updated my ratings.

Oh, I get it! (after reading the comment above)

Yeah, some quality of life improvements could make a difference, like adding an "error" sound when you press space but you can't jump, increasing the pill's hitbox, and making the music persistent. Or muting it while you're dead, if you want to keep this feeling of "…oh.". And it continues where it is/stopped. That can make music loops more than 5 seconds long more interesting.

But overall a good start!