Murky Oil of Speed

Murky Oil of Speed don't increase the speed of the character. Instead they give the consumer the status effect of feeblemind. The effects lasts for 5 minutes. This item appears in Baldur's Gate, Baldur's Gate: Enhanced Edition and Baldur's Gate II.

In-game description
"This oddly murky oil would appear increase the movement and combat capabilities of the imbiber by 100%. Thus, a movement rate of 9, becomes 18, and a character normally able to attack once in a round attacks twice.  This does not reduce spellcasting time however. The duration of the effect is 5 turns."