What is "go pill"

n. (context informal English) An amphetamine tablet.

A go pill refers to a wakefulness-promoting agent used for fatigue management, especially in a military combat-readiness context; this is contrasted with a no-go pill, which is used to promote sleep in support of combat operations. A go pill generally contains one of the following drugs:

• Amphetamine ( methamphetamine having been used historically, such as during the Second World War), which is a strong psychostimulant drug; no longer approved officially for use by the U.S. Air Force, possibly due to safety concerns brought up in the wake of incidents like the Tarnak Farm incident.
• Modafinil, a wakefulness-promoting drug (or eugeroic)