Throughout the game, you’ll find a variety of useful items that will help you to either heal, or kill zombies. Below is a list of each item, along with a brief description.
The medical kit will heal 80 percent of your injuries, restoring your health from red or yellow, to green. You can either heal yourself, or heal teammates, with medical kits. If you get incapacitated three times in a row, without using one, you’ll die, so make sure to use one before the third time. Medical kits can be found throughout the game, however they are most often found in safe rooms and / or medicine cabinets. The medical kit is only good for one use.
The defibrillator is used to revive a dead teammate. It should be noted, however, that dead teammates will respawn in closets, later, so I wouldn’t worry too much about using defibrillators. It usually takes about 3 seconds, and then, after you use this item, your dead teammates are back to life. Just like the medical kit, it’s only good for one use.
Pain pills boost your health, by 50 percent. Over time, however, that boost will slowly diminish, so be sure to heal with a medical kit, as soon as you can. In tough zombie battles, pills can mean the difference between making it to the next safe room, and death. So, look for them and grab them, wherever you find them. I usually find them on the ground, on / under tables, or in medicine cabinets.
The adrenaline shot boosts your health, by 25 percent. Over time, that boost will slowly diminish, just like with pain pills. However, with the adrenaline shot, you can use items in only half the time it would normally take you. Also, you can run faster, rescue and revive teammates faster, and zombie attacks won’t slow you down.
With the explosive ammo upgrade, your shots will explode after they’re fired, causing more damage, in a wider area. This is good for regular infected, as well as the weaker members of the special infected. Just for fun, try shooting a special infected in the head, with the explosive ammo equipped, and see what happens.
With the incendiary ammo upgrade, your shots will cause the zombies they hit to catch on fire, greatly weakening them. This is good for the tougher members of the special infected, like tanks or witches, that would otherwise be nearly impossible to defeat, with a zombie horde headed your way.