When using a stim, healing / status effect item or food, the inventory of that item ticks down by one with each item you use. However, there is a way to not lose the same item you consume.

The window to perform this glitch is actually quite large. If you drop the item after you consume it and before the game updates the inventory of that item, the item will then be on the ground, and you still have the status effects from that consumable.

So basically, you can take advantage of the game's slow updating system in order to achieve infinite consumables.

There is an exception to thrown weapons, flares, rope, and bombs.

If you're still confused, maybe this video will help you visualize it better.

Give all credit to LufiaGuy2000, he discovered this bug and explained how it works!