it depends on the dosage strength of xanax and trazodone that he is taking. first of all please be informed that both these drugs must only be taken when prescribed by a doctor. if it is then you can check his prescription to know if he is taking then as prescribed or abusing them already. Just to give you an idea however, here are the usual adult dose of these drugs.
Short-term management of anxiety
0.25-0.5 mg tid, increased to 3-4 mg daily if necessary.
Up to 10 mg daily.
Initially, 150 mg daily increased by 50-mg increments every 3-4 days up to 300-400 mg daily if necessary. Daily dosage may be given in divided doses or as a single dose at night. Max: 600 mg daily in divided doses in severely depressed patients.
Initially, 75 mg daily increased to 300 mg daily if necessary. Daily dosage may be given in divided doses or as a single dose at night.
going over their drug interactions however does not show direct antagonism or potentiation.
source of dose: mims