The Outer Worlds has a unique system for consumables in the game There are many different types of consumables that you can use which have varying effects on your character. There are two different and unique ways to use consumables in The Outer Worlds. You can either use them from the consumables menu, OR, you can add them to your inhaler.
Head into your Inventory and stock the inhaler
When you head to the Consumables screen you will slots at the top of the screen. The left slot will always be your Adreno health inhaler units. The other slots are unlockable and then you can put consumables in these slots. The capacity and the effectiveness are based on your medical skill. The higher you raise that skill the more slots you’ll unlock.
Consumables can be used in the inventory screen as well
But you can basically put any of the consumables that you find in the game into the inhaler and use them on the fly when out in the world. For example, if you hit the inhaler like normal you will get a health boost, plus whatever the other consumables you have slotted into the inhaler. However, if you use the item in the menu you can use them one by one.
To get all four slots for the inhaler opened you actually need to increase your medical skill to level 80.