Adrenaline Shot

Adrenaline is included in Left 4 Dead 2, occupying the pain pills' inventory slot. Upon injection, the user gains 25 temporary health; and for 15 seconds, they move faster, do not experience melee fatigue, and are immune to the horde's slowing melee attacks.

It also increases the speed of using health kits, reviving survivors, and switching weapons and items. As temporary side effects, the user also experiences tunnel vision, and sound becomes monophonic, hindering their ability to determine the direction from which a sound came. This can become annoying during a split screen campaign, if one player uses the Adrenaline injector too much, as the monophonic penalty affects both players.

The Adrenaline injector is always seen in the Crescendo event in "The Park". This item could become valuable at the end of a finale, where Survivors must reach a rescue vehicle while being impeded by the horde. Like Pain pills, the Adrenaline injector can be passed to a teammate by using the melee button.

The health added by the injector appears to drop slower than the health from pills, although there is no console command to confirm this.

Trivia

 * Adrenaline no longer causes the user's health to go above 100hp . If the player has 80 health and uses the Adrenaline, his/her health goes to 100, and then quickly drops down to 99.