When a person with a mental illness commits a crime, the legal system doesn’t follow a single path. What happens depends on the severity of the illness, the nature of the crime, and the state where it occurred. The person may be diverted out of the criminal system entirely, evaluated for their ability to participate in a trial, or tried and sentenced like any other defendant. Mental illness alone does not exempt someone from criminal responsibility.
The First Question: Can This Person Stand Trial?
Before anything else moves forward, the court needs to know whether the defendant is mentally capable of participating in their own defense. This evaluation, called a competency assessment, isn’t about whether the person was mentally ill when the crime happened. It’s about their mental state right now, during legal proceedings.
The standard comes from a 1960 Supreme Court case, Dusky v. United States, which established that a defendant must have a “sufficient present ability to consult with his attorney with a reasonable degree of rational understanding” and a “rational as well as factual understanding of proceedings against him.” In practical terms, evaluators are looking at whether the person understands the charges against them, grasps the roles of the judge, jury, prosecutor, and their own lawyer, and can work with their attorney to make decisions about things like how to plead or whether to accept a plea deal.
A person might understand the legal system in the abstract but still fail the competency standard. Someone experiencing delusions, for example, might be able to explain how a trial works but be unable to apply that knowledge to their own situation because they believe the judge is secretly working for an intelligence agency. Evaluators assess not just knowledge but reasoning and the ability to weigh information realistically.
What Happens If Someone Is Found Incompetent
If a defendant is found incompetent to stand trial, the charges aren’t dropped. Instead, the court orders what’s known as competency restoration, a process designed to treat the person’s mental illness enough that they can meaningfully participate in their defense. This typically means psychiatric treatment, most often medication for conditions like schizophrenia or severe bipolar disorder.
Where restoration happens varies by jurisdiction and the seriousness of the charge. People facing felony charges are more likely to be sent to an inpatient psychiatric facility. Those charged with misdemeanors may be placed in outpatient programs. Some states run restoration programs inside jails, though these have drawn criticism for prioritizing security over treatment. The jail environment can work against recovery, and many county facilities avoid using involuntary medication altogether because of the ethical and legal complications involved.
Forced medication is a particularly fraught issue. The Supreme Court’s 2003 decision in Sell v. United States laid out strict conditions: the government must prove that important interests are at stake (typically meaning serious charges), that the medication is substantially likely to restore competency, that its side effects won’t undermine the person’s ability to participate in proceedings, and that the treatment is medically appropriate. All four conditions must be met by clear and convincing evidence.
If restoration works, the person is returned to court to face trial. If it doesn’t, and the person is deemed “nonrestorable,” the criminal charges may eventually be dismissed, though the person can be involuntarily committed to a psychiatric facility through civil proceedings if they’re considered a danger to themselves or others. Extended delays in getting treatment actually make nonrestorability more likely, creating a painful irony in systems with long waitlists for psychiatric beds.
The Insanity Defense
The insanity defense is probably the most misunderstood part of this process. It’s raised in less than 1 percent of criminal cases and succeeds even more rarely. It’s also completely separate from competency. Competency asks whether you can participate in your trial today. The insanity defense asks whether you were so mentally impaired at the time of the crime that you shouldn’t be held criminally responsible for it.
Most states use some version of the M’Naghten Rule, which dates back to 1843. Under this standard, a defendant is not guilty by reason of insanity if, because of a mental disease or defect, they didn’t know the nature of what they were doing or didn’t know it was wrong. This is a narrow, cognition-focused test. Knowing that you were stabbing someone but believing God commanded you to do it might qualify. Knowing you were committing a crime but feeling unable to stop yourself generally would not, at least not under M’Naghten alone.
Some states use a broader standard from the Model Penal Code, which adds a volitional component. Under this rule, a defendant isn’t responsible if they lacked the “substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law.” The word “appreciate” is intentionally broader than “know,” recognizing that mental illness exists on a spectrum rather than in absolutes. The second half of the test captures situations where a person understood what they were doing was wrong but genuinely could not control their behavior.
Six states have essentially abolished the insanity defense altogether: Idaho, Kansas, Montana, Nevada, North Dakota, and Utah. In those states, mental illness can still be raised as evidence during trial, but there is no formal verdict of “not guilty by reason of insanity.”
What “Not Guilty by Reason of Insanity” Actually Means
A successful insanity defense does not mean walking free. People found not guilty by reason of insanity (NGRI) are almost always committed to a secure psychiatric facility, sometimes for longer than they would have spent in prison for the same offense. Release depends on demonstrating that the person is no longer dangerous, which requires ongoing evaluation and, in many jurisdictions, court approval.
The outcomes for people who go through this process are, on the whole, better than many assume. A 25-year follow-up study of people charged with murder found that those acquitted by reason of insanity were released to the community earlier than those who went to prison for the same crime, and they had a lower rate of reoffending. People with severe mental illness who were convicted and sent to prison, by contrast, were held longer before parole but did not show higher recidivism rates once released. The data suggests that structured psychiatric treatment followed by supervised release produces at least as good, and often better, public safety outcomes as incarceration.
Mental Health Courts and Diversion
For lower-level offenses, many jurisdictions now offer an alternative path before the case ever reaches a traditional courtroom. Mental health courts are specialized programs that connect defendants to treatment instead of cycling them through jail and back onto the street. Eligibility typically requires that the person has a diagnosed mental illness connected to their criminal behavior and that their participation won’t pose an increased risk to public safety.
These courts operate on a supervision model. A defendant agrees to follow a treatment plan, which might include medication, therapy, housing assistance, and regular check-ins with a judge. If they complete the program, charges may be reduced or dismissed. If they don’t comply, the case returns to the standard criminal process. The goal is to address the underlying condition driving the behavior rather than simply punishing the behavior itself.
The Reality Inside Prisons
For the majority of people with mental illness who commit crimes, none of the above pathways apply. Most are found competent, don’t raise an insanity defense, and are convicted and sentenced like anyone else. This is where the numbers become stark. A systematic review covering nearly 59,000 incarcerated people across 43 countries estimated that about one in seven people in prison has a severe mental illness. The prevalence of depression among incarcerated people is roughly 12.8 percent. Psychotic disorders, including schizophrenia, affect about 4.1 percent of the prison population, a rate many times higher than in the general public.
These individuals are technically entitled to mental health treatment while incarcerated, but the quality and availability of that care varies enormously. Many end up in solitary confinement during psychiatric crises, which worsens their condition. Upon release, gaps in community mental health services make reoffending more likely, not because mental illness itself predicts violence, but because untreated illness combined with homelessness, substance use, and a lack of support creates a cycle that’s difficult to break.