How do a psychologist and a psychiatrist differ?

Doc's: Psychiatrist finished medical school & obtained md degree. Psychologist finished training & received phd degree, can diagnose illnesses but cannot prescribe medications, while md can.

Therapy vs meds: Speaking very generally, most psychologists hold either a PhD or a PsyD degree (I hold both) and practice psychotherapy. Psychiatrists hold either an MD or a DO degree, and they prescribe psychotropic medications, and generally do not do all that much therapy these days, but years ago psychiatrists would do both.