Kingsajz [1] is one of my favorite Polish movies of all time. It's about way for people to consume some elixir and become tiny (it's an adult movie, although may not sound like it). The special effects are absolutely phenomenal - it's mind boggling that it was done in 1987, and with communist budgets! Unfortunately looks like no English subtitles are available.

[1] https://35mm.online/vod/fabula/kingsajz