Tonic Slots allow the player to equip passive Gene Tonics. Tonic slot upgrades allow the player to carry one more tonic per slot purchased.
The player begins the game with two slots in each of the three track types. Each track's slots can be extended separately by purchasing different slot upgrades from Gatherer's Garden machines found during the exploration of Rapture. Each of the slots cost 80 ADAM and, not unlike Plasmid Slot upgrades, the price does not change. Identically to the Plasmid Slot line, the maximum is six slots per track. The player can purchase a maximum of twelve tonic slots, an additional four per track. On the Xbox 360 and PS3 versions of the game, an achievement and a trophy is unlocked for acquiring all of the slots in a track.
Tonic slots return as a purchasable upgrade. The player begins with four open tonic slots. The initial price for the first five purchases is 25 ADAM. It then increases to 35 ADAM for the next four successive purchases. The final five slots cost 45 ADAM each. A maximum eighteen slots are available, and there is no longer any distinction between tonic types, thus the player may assign any tonic to any slot.
Player loadouts are fixed at three tonic slots.