It can be purchased from most general stores, either from the shelf or the catalog, as well as found out in the world.
Drinking one doubles the Hair Growth rate of the player. The effect stacks - drinking 2 speeds up the rate to 4, drinking 3 increases it to 8 etc - and ends once the next stage of growth is achieved.
The player's hair and facial hair will only naturally grow to a length of 7, but hair tonic can increase the beard's growth up to a 10. Levels 8 and 9 take roughly two weeks to reach with one dose of tonic each, while reaching a level 10 beard takes roughly 3 weeks of in-game time.
- Until beard stage 5, consuming more than 3 at a time is considered wasteful, as the time required to progress to the next stage is relatively short. However, from this point onward the growth progress normally takes up several in-game weeks, so taking more than 3 can speed up the progress considerably.
- The player needs to trigger a "screen fade" to allow the hair/beard progress to the next stage; they do not grow in real time, and the progress will happen "off-screen", such as while sleeping or fast traveling.