From Pathfinder Gamemastery Guide, which isn't enabled.

Zerk

ITEM 4

ALCHEMICAL CONSUMABLE DRUG INJURY POISON

Price 20 gp

Usage held in 1 hand

Bulk L

Category drug

This bitter paste is used among some gladiatorial rings for its short-term benefits in a fight.

Activate Interact (Injury)

Saving Throw DC 20 Fortitude

Maximum Duration 1 hour

Stage 1 +2 item bonus to Perception rolls for initiative, and if you have an addiction to zerk, your melee weapon and unarmed attacks deal an extra 2 damage during the first round of a combat encounter (1 minute)

Stage 2 Drained 1 (1 hour)

Pathfinder Gamemastery GuideOGL