Health Enhancements
You can carry either Adrenaline or Pain Pills in one of your inventory slots, but not both at the same time. Use them if you need them, but do this quickly, as you have no offensive capabilities while you’re holding either item.
Adrenaline
Jab a syringe into yourself to instantly receive a +25 Health boost, slight tunnel vision, and a sharp view of your surroundings. This boost gradually diminishes, and cannot take your Health over its maximum. It also gives you a speed boost.
Adrenaline is useful mainly to cover distances much more quickly than normal (and secondarily, to receive a Health boost), as it has the added effect of maximizing your speed. It also allows you to shrug off Common Infected attacks that usually slow you down.
Use Adrenaline when you need to cover ground, either to escape an area or to sprint through a highly dangerous zone to a switch that needs pressing. You also may wish to use it when facing a large entity such as a Tank, to slightly quicken your strafing capabilities. Adrenaline is also great to use to revive, heal, defib, or pour faster.
Pain Pills
When taken, Pain Pills add 50 points to your Health, however, this fix isn’t permanent.
This item is designed to give you a temporary boost in Health if you’ve been wounded, and don’t want to use (or don’t have) a First Aid Kit. The boost shows up visually in your Health bar (which slowly decreases back to the wounded state you were in before popping the Pills).
Any mobility issues are healed, but if you take damage, your “lower” Health (the level prior to receiving the pills) takes the hit. Find a First Aid Kit to heal “properly,” but don’t do this immediately, as this would simply waste the Pills’ boost.