Not a complete answer, but: It’s erasing without intent to rewrite, so it’s Rabbinic in nature. Not all Rabbinic prohibitions are permitted for non-life-threatening ailments, but many are, and a general rule of thumb (there are exceptions) is that a decree lest you violate a Biblical prohibition is always permitted for these ailments. There’s a bunch of other factors to consider here, but I would bet there’s no issue whatsoever given that the person is already permitted to take the medicine.

What about animal crackers :-)

@robev In all seriousness, I think animal crackers would be fine. The prohibition is specifically "writing". That being said, anecdote time: When the New Orleans Saints won the Superbowl, a member sponsored a Kiddush in their honor and had a special cake made. Everyone knew letters were a problem, but the Rabbi & Assistant Rabbi had a discussion regarding some other symbols on the cake. I believe the ruling was to "pre-cut" some of the items to play it safe. But the punchline was...

The Gemarah anticipated many things relating to the modern world, but they never expected that the Saints would win the Superbowl!

Erasing a symbol or drawing is no less than erasing a letter. I'm pointing out eating food shaped like something (let's say the letter A) is potentially included in the question

@manasseh No, the prohibition is not specifically writing. Drawing meaningful pictures is equally prohibited.