There is a website called What A Difference that has a lot of good information about this very topic. I’ve seen the advertisements on TV and the site says they’ve also made ads for radio, although I personally haven’t heard any. But a lot of people haven’t seen or heard the ads or discovered the website. So here, as concisely as I can, I’m going to enumerate, from the point of view of a person with mental illness, how to behave if someone you know tells you zie has a mental illness.
First off, because of the way society at large views people with mental illnesses, zie has probably spent a lot of time considering whether to tell you about zir diagnosis. Zie may be afraid that you will drop zie as a friend or, if zie is a family member, refuse to see zie or refuse to allow zie near the children or something like that. So remember that it takes a lot of courage and trust for a person with a mental illness (or several mental illnesses) to come to you in the first place and tell you about zir diagnosis. Chances are, you’ve known zie for a while now, or else zie wouldn’t trust you enough to tell you.
Secondly, given that you and zie have probably known one another for a while, zie has probably known about zir diagnosis or diagnoses for some time and has probably been experiencing symptoms before diagnosis (if zie didn’t have any symptoms, why would zie see a mental health care provider to get a diagnosis in the first place?). So zie has been a person with mental illness for a while now, and zie has been your friend, relative, coworker, classmate, or what-have-you all this time; are you going to treat zie differently just because you know something about zie that you didn’t know before? If zie told you something else about zirself that did not indicate zie was involved in any sort of criminal or exploitative activity, like zie collects seashells of the exact color of the complexion of zir first sexual partner (just for something admittedly a mite unusual that nonetheless means nothing harmful), would that change whether zie is a good friend (or loving relative, or competent coworker or interesting classmate or what-have-you)? Whatever drew you and zie together has not changed because zie has told you zie has a mental illness. Zie is still the same person you’ve known and cared about for however long you’ve known and cared about each other.
Third, please do not broadcast zir diagnosis to everybody you both know. Having a mental illness is really not a good cause for feeling ashamed, since having a mental illness does not mean someone is violent, stupid, weak-willed, or a bad person, simply that zie has a medical condition over which zie has little if any control, just as if zie had diabetes, or epilepsy, or an allergy to peanuts. However, the world at large tends to treat people with mental illnesses as if the state of having a mental illness somehow makes someone a bad person, and thus, a lot of people with mental illnesses are hesitant to let it be known that they have a mental illness (or more than one). Let zie choose whom zie wishes to tell about zir diagnosis.
Last, and most important, just be there for zie. Be zir friend, or relative, or coworker, or classmate, or what-have-you. Have lunch together. Talk on the phone. Text zie. Keep zie on your Facebook friends list. Just be there. Accept zie for who zie is. I cannot stress enough how important it is for people with mental illnesses to have people in their lives who care about them and support them by just being there.
Your friend (or relative or coworker or classmate or what-have-you) is still your friend (or whatever zie has always been to you). Don’t treat zie any differently because zie has had the courage to trust you with zir diagnosis.