Instructions
Purchase a Catalyst Chemistry Lab Station for your Sim's home and place it in a room where it is easily accessible to your Sim.
Click on the table to have your Sim begin brewing a potion or learning new potions. Your Sim's Logic skill is tied to his ability to learn new potions. The higher his Logic, the less likely that a new potion will turn out to be a failure.
Click on the potion when it has finished brewing and select the "Mix Potions into Drinks" option from the menu. This disguises the potion as a Mysterious Drink that looks like an ordinary mixed drink. If this option does not appear, increase your Sim's Logic levels by brewing more potions, reading books on Logic or using a chess set or telescope.
Click on the Mysterious Drink and to put it in your Sim's inventory. Open Build and Buy Mode, select the Mysterious Drink from your Sim's inventory and place it on a counter. Guest Sims will eventually help themselves to the drink, causing the effects of the potion to activate.