The Syringe is a special item used in
Guns of the Patriots to raise Snake's
Psyche level and to defeat the bosses Vamp and Screaming Mantis. After gaining the Syringe in Act 2 from Naomi, you can use the syringe to artificially raise Snake's Psyche level for ten uses. After ten uses, Snake's Psyche level will increase temporarily and then drop lower than it was before. Additionally, the Syringe is used in a secret way to defeat Vamp in Act 4: when Vamp falls, sneak up behind him with the Syringe equipped. When he stands, hold "R1" to grab him from behind, and then press the "Triangle" to inject him with the Syringe. In Act 5, the Syringe also comes in handy against Screaming Mantis. When you notice that Screaming Mantis is psychically pushing all of your shots away, use the Syringe on Snake to free him from her control.