The concept of a "pill" in ASL is generally expressed by just fingerspelling the letters "P-I-L-L."
Another sign is to use a "G"-handshape as a classifier to mime holding a "pill" between the tips of your index finger and thumb.
There is a sign that means "take a pill." It looks as if you are flicking a pill into your mouth.
PILL: "take a pill" (verb form)
You could do a smaller double movement (repetition) of this sign to change it from a verb into a noun. Or if you do two or more larger (full movements) to indicate a process of taking pills (as in describing the behavior of someone who is always popping pills).
Notes: