The options vary somewhat among the service branches, but when adequate rest is insufficient and relief crew are not available, two basic options are available to help flight crew remain alert during long missions: caffeine and “Go Pills.” All of the services recommend the use of caffeine over Go Pills, reserving the latter for situations when all other fatigue countermeasures have been exhausted or have been determined inadequate for the immediate situation.

Go Pills are prescription medications (dextroamphetamine or modafinil), so they can only be dispensed by a flight surgeon. In addition, they must be ground tested by each individual (with flight surgeon supervision), sufficiently in advance of need, to determine individual tolerance and dosing, followed by a specified period of non-flight status. The use of Go Pills (and ground testing) is optional.

The type of Go Pill approved for use also depends in some cases on the type of aircraft. In general, the controls on the use of dextroamphetamine are more strict than those for the use of modafinil, which (for example) the Official Air Force Aerospace Medicine Approved Medications  list approves for use by all flight crew with a few exceptions. Navy policy also supports modafinil as preferred over dextroamphetamine. The Army has not yet approved the use of modafinil.

All services support and encourage the use of caffeine before Go Pills. Guidance from the services varies but in general the recommended amount for vigilance is up to 200 mg caffeine at intervals of 3 to 4 hours, with a maximum of 800 mg over the course of 24 hours. Forms of caffeine convenient for in-flight use include caffeine gum and caffeine pills, but the latter requires prescription and dispensation by the flight surgeon.

All services prohibit the use of most dietary supplements by flight crew, including performance enhancers and energy drinks. Exceptions can be considered but require much discussion (such as flight surgeon approval).

Branch Policy Documents (current as of date of posting) and other guidance

Air Force


  • NAVMED P-6410: Performance Maintenance During Continuous Flight Operations (1 January 2000)
  • U.S. Navy Aeromedical Reference and Waiver Guide (11 August 2021)
  • BUMED Instruction 6410.9A (6 May 2016)


  • AR 95-1 Aviation Flight Regulations (22 March 2018)
  • AR 40-8 Temporary Flying Restrictions Due to Exogenous Factors Affecting Aircrew Efficiency (22 March 2019)

Other guidance

Updated 6 May 2020