Mental Illness & the Insanity Defense Statistics [2024 Updated]

Nellie L. King

For individuals suffering from mental illness, their condition can sometimes significantly impact their behavior. Depending on the type of mental illness an individual is suffering from, they could lose their ability to think rationally and understand the difference between right and wrong in certain instances. Many states allow defendants in criminal cases to plead not guilty by reason of insanity, or NGRI. Learn more about mental illness and the insanity defense statistics.

Does Mental Illness Disqualify You from Criminal Prosecution?

While states like Florida provide the option to use mental illness as a defense in criminal cases, that does not mean an individual who is mentally ill will be automatically disqualified from criminal prosecution. The defendant must prove they were insane at the time they allegedly committed the crime because the standard in many courts is to presume sanity as a default mental health state.

It’s important to keep in mind that a successful insanity plea does not mean the defendant will be free from consequences. In certain instances, the court might require defendants who are found not guilty by reason of insanity in criminal cases to undergo mental health treatment instead of jail time. An acquitted defendant who pleads insanity could be committed involuntarily to in-patient treatment at a mental health facility for a length of time at the discretion of the judge.

While mandatory treatment in a mental health facility or institution could be seen as a form of punishment by some, the acquitted defendant could greatly benefit from professional mental health treatment. The option of pleading insanity gives those who are suffering from mental illness the opportunity to receive the professional medical intervention they might desperately need and alleviate the symptoms of their mental health condition for a better quality of life.

Insanity Defense Success Statistics

Insanity can be extremely difficult to prove. In fact, less than 1% of defendants in criminal cases plead insanity as their defense in the United States, and only about .26% of those who plead insanity are successful in their plea, according to the same source. Each year, only about 30 defendants in America succeed with their insanity plea.

These statistics show why it can be extremely beneficial for defendants in criminal cases to hire a criminal defense attorney who has knowledge of the legal requirements for claiming mental illness as a defense strategy.

In terms of criminal defense, insanity is not a medical diagnosis but is instead a legal term. However, testimonies from mental health professionals or copies of a defendant’s medical records might be used as evidence to prove they were insane at the time of their alleged crime. Certain pre-existing mental health conditions that could bolster an insanity plea might include a diagnosis of bipolar disorder, post-traumatic stress disorder (PTSD), or schizophrenia.

Proving Insanity in Florida Criminal Cases

In the state of Florida, defendants in criminal cases citing mental illness as their defense must prove insanity per the standards of the M’Naghten Rule. According to this rule, the defendant must prove in court that they did not have the ability to understand the consequences of their actions, or they understood the consequences but couldn’t recognize their actions were wrong.

There are significant legal nuances to proving insanity according to the M’Naghten rule. Specifically, the definition of what’s right and wrong could be somewhat of a gray area for respective individuals who are serving on a jury and responsible for reaching a verdict. For these reasons, hiring a criminal defense attorney is advisable if you’re considering pleading insanity in a criminal case.


Q: What Are the Statistics of the Insanity Defense?

A: The statistics of the insanity defense are that only about 1% of defendants citing mental illness in criminal cases are successful in their plea. Another statistic of the insanity defense is that it is successful in roughly only 30 cases annually. Many of those who successfully plead insanity in criminal cases do not go free and face involuntary commitment to a mental health facility or institution for long periods of time.

Q: What Is the Risk of Using the Insanity Defense?

A: One risk of using the insanity defense is that the jury will not believe the defendant, and they will be found guilty of the crime. Other risks are that the defendant will be found not guilty by reason of insanity or found not competent to stand trial, and will be sent for treatment in a mental health facility for an uncertain amount of time.

Q: How Successful Is the Mental Disorder Defense?

A: The mental disorder defense is not successful in most cases. Of the roughly 1% of criminal defendants who plead insanity, only .26% are found not guilty by reason of insanity. While these statistics might not seem favorable for those pleading insanity, citing mental illness as a defense could be beneficial in some criminal cases. Individuals considering pleading insanity as a defense in criminal court proceedings should work with an attorney to understand their options.

Q: What Are the Benefits of Using the Mental Disorder Defense?

A: One benefit of using the insanity defense is that the defendant can seek treatment for mental illness rather than being incarcerated and not getting the treatment required to help the individual. When an untreated person is released from prison, they will be more likely to commit another crime than if they are able to treat their mental illness and get the help they need.

Trust the Law Offices of Nellie L. King for Defense in Criminal Cases

If you or a loved one is facing a criminal case and want to understand the options for pleading not guilty by reason of insanity in the state of Florida, you need an experienced attorney who understands the laws and requirements for this type of plea. Our legal team understands the impact that mental health can have on peoples’ lives and will work with compassion on your unique circumstances.

Contact the Law Offices of Nellie L. King today for a case evaluation and take the first step toward determining a legal strategy for challenging your criminal charge in court.

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