This shows a slightly different angle.

This is the marking on it. No other maker's mark or any sort of identification.

Since 4 centiliters equals about 2 1/2 oz....I would guess it's a cute little novelty shot glass.

Or could it be a medicine/potion dispenser, kind of like the invalid feeding bowls?

Crack cocaine pipe? Looks like something i've seen used by a druggie on Intervention. I'll be interested to find out. ;o)

It's a shot glass.....see the link.

Here is a link that might be useful: shot glass

Why would it need a hole to inhale if it were a shot glass, and such a small hole?

The thought crossed my mind that they may be shot glasses, but I've never seen one measured "4 cl". Also, the glass is textured all around except for an untextured space 2" x 1". Like maybe for a label or something. Also, it seems like there's a seam dividing the glass including the stem. But it is very well done and smooth. Almost invisible.

Think I'm not using the technical terms here.

Unless you have been seeing European shot glasses, likely you have not seen one that measures in metric.
According to the link, you suck it down....and likely the blank space in the texturing did hold a lable.