I'm going to give you a very long winded answer that circles around the issue.
Guy believes he is Abraham Lincoln. Every shrink that meets with the guy comes out with the same diagnosis and in everyday speak, everybody agrees he's flat out crazy. Guy who everybody admits is crazy commits a murder. Does the fact he's crazy as a loon matter?
NO! The only way that it is relevant that he is crazy is if he kills someone thinking that person is John Wilkes Booth, and he is killing that person in self-defense.
Insanity defenses and lack of competence (two entirely different legal and medical issues) are rare defenses. Insanity defenses require very specific conditions to work.
Nearly everyone in prison has some significant mental health pathology. However, that pathology is also shown by a significant number of people who have never been to prison. For example, I know a couple of murderers who have a significant anit-social personality disorder (ASPD), which includes sociopathy and psychopathy behavior. I know a lot more people who have never arrested that, absent the murder component, have a pathology that is much stronger then the guys in prison.
There are a lot of drugs that can cause delusions and breaks with reality. However, there's significant evidence that the ICU, absent drugs, can cause a break with reality and delusions.
But let's look at a common drug group that is a popular legal defense at the moment. Steroids, or more commonly now, roids. Roids can cause heightened aggression and delusions. Roids can be legally prescribed or illegal, or a person can mix it up. Roids have been viewed as a factor in several assaults and murders.
I have not heard of a successful roid defense. It's a Twinkie defense used by defense attorneys when they have nothing. Understand that a defense attorney, when their client insists on trying a hopeless case, can not get up in front of a judge and say they've got nothing. You grab the Twinkie, cash the check, and figure your client was going to prison for a long time no matter what you do.
So repeating what was discussed in your other thread, unless you're doing a novel about bad roids (or whatever drug), don't worry about the drug. Morphine is a nice drug that is prescribed and causes many issues. Use it and don't get fancy. Write your book and then, if you have to, figure out what drug would cause the specific symptoms that developed in your story.
Best of luck,
Jim Clark-Dawe
