Graph overlay that doesn’t obscure the data

I'm building an app that renders a line graph of the user's wellness over time.

(For example:)

_{(source: netdna-cdn.com)}

It also needs to mark the days they took medication. Originally, I wanted to place a dot at the bottom of the graph on any day the user took meds, but I also don't want to limit the number of medications they're tracking, and stacking dots doesn't work too well.

How would you represent that concept?