Most medicine has expiration dates. If he needs it only every 3-5 years, it's unlikely the pills will still be usable.
Pills (and chemicals) are not SSL certificates: they don't cease to work at the expiration date + 1 second.
Maybe a liquid medicine would go bad but I suspect pills are forever.
I know I read somewhere about morphine pills from WW2 medkits being found to still be useful 60+ years later - like say 30-50% of stated dose.
Yes it will. The pills don't actually expire. They will work unchanged for decades.
See: https://www.health.harvard.edu/staying-healthy/drug-expirati...