Perhaps said friend is on medications that prevent him from feeling high. i tried Welbutrin (a dopamine reuptake inhibitor, therefore desensitizing my neurons to dopamine because of the elevated amount) and smoking a whole blunt barely got me stoned. Antipsychotic meds will also inhibit the high.

Try making him some Green Dragon. If you don't wanna cook the herb up, just let a half ounce of reg/mid sit in a fifth 100+ proof alcohol for a month (the higher proof the better; I use Bacardi 151 or Everclear). If this doesn't get him stoned, then that sucks for him lol.