A potion of speed increases 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 but once per round would gain double attacks in a round. 

Note that this does not reduce spell casting time, however (cf. haste spell). 

Use of a speed potion ages the individual by 1 year. 

The other effects last for 5-20 rounds, the aging is permanent.