It sounds like your brother is suffering from paranoid schizophrenia. It usually appears in the late teens. Check him into your local mental hospital. If he endangering himself or others, they can commit him against his will for a few days at least. Call the psychiatric until at your local hospital to get more information. Your/his parents aren't doing him any favors by refusing to get him help if he's obviously showing signs of delusional behavior.
its not easy to see someone you love being hurt, but you need to do the right thing. illegal drugs have a strong indorphin content, and it is not unusual for these side affects to occur. What i suggest you do, is put him in a medically approved home, where he can be monitored, and watched, as the drugs filter out of his system, and all this while keeping him away from the drugs he is addicted to. its not an easy road, not a pleasant one, but one you will be glad you took.
Call your local police department too. They may have more information. If he is hurting himself he may hurt someone else without even really knowing it and the police department surely wants to avoid that. But, hey get him help. He is crying out for it. Don't let it go.
No, DO NOT "call your local police department".
This is in no way a matter for the criminal justice system.
This will provide grounds for a search warant for your brother's living quarters, as well as entering him into the NCIC data base of suspected drug dealers. There is no confidentiality and you may be forced to testify against him in a court proceeding that may result in his imprisonment.
It is unfortunate, but you have no standing to order his commitment or to enforce any medical proceedings. He is nineteen years old and an adult.
Whiule his behavior is self-destructive and disturbing, there is nothing to suggest he is suicidal or in danger of harming others. These are the two generally accepted criterion for mandatory institutionalization for psychiatric evaluation.
Unless these is outward evidence of such behavior, it will require his agreement for period of psychiatric observation.
The best thing to do is to talk to him and get him to agree to an evaluation.