Cold and flu season is here.

For Aviation safety, pilots should not fly following the last dose of any medications until a period of time has elapsed equal to: A. 5-times the maximum pharmacologic half-life of the medication (preferred); or B. 5-times the maximum hour dose interval if pharmacologic half-life information is not available. For example, there is a 30-hour wait time for a medication that is taken every 4 to 6 hours. If there is a range, calculate by using the higher number (e.g., 6 hours x 5 = 30 hours No Fly wait time).

https://www.faa.gov/ame_guide/media/DNI_DNF_tables.pdf