When adult children have mental health problems there isn't a lot a parent can do, unless they make a specific threat that they will hurt themselves or someone else. Or you. Calling police (dicey) or a mental health intervention service that works with police (much better) might get a 72-hour hold in a hospital psych ward, but beyond that, the control is in the hands of the grown child.

In college I rented the downstairs apartment in a house owned by friends who lived upstairs. They had an adult son who needed a diagnosis and medications but it took a while before it finally happened for him. If I was home and I heard a pattern of loud stomps on the ceiling I was to race outside, around the back of the house, and up to their back door and let myself in. That happened a couple of times (once it was because the pigs got out of their enclosure and I had to help round them up) before it finally worked - Tommy was there, he was so angry and hurt and sad all at once, and made a declaration that he would kill himself or them - so when the sheriff arrived I was the witness. ("Please don't cuff him tightly, he's ill, not a criminal!") That 72 hours made a difference and started him on a path of treatment. Last I heard he has a normal life and a family of his own. It can work. I hope it does for your son also.