How to plead “not guilty by reason of insanity” in California

Under California’s insanity defense, you cannot be convicted of a crime if you were legally insane when you committed it.

California’s test for insanity is the “M’Naghten rule. To win on this defense, you must prove at trial that it is “more likely than not” that you either:

1. Did not understand the nature of your criminal act OR
2. Did not understand that what you were doing was morally wrong.

Then if the jury finds you “not guilty by reason of insanity,” you will be committed to a state mental hospital instead of being sent to prison.

Examples

• A delusional woman steals her neighbor’s vacuum, which she believed belonged to her. Since she did not understand she was taking someone’s property, the insanity defense may work for her.
• A schizophrenic man grabs a boy from the park and takes him to ice cream because he believes God told him to. When the man is later charged with kidnapping, he can claim insanity because he did not understand that what he was doing was morally wrong.

In this article, our Los Angeles criminal defense attorneys will discuss the following key issues regarding insanity laws in California:

• 1. The M’Naghten Test
• 2. Proving Insanity
• 3. The Plea
• 4. Sentencing
• Frequently Asked Questions
• Additional Resources

1. The M’Naghten Test

Under California law, you are “legally insane” if, because of a mental illness, you either:

1. Cannot understand the nature of your criminal act OR
2. Cannot distinguish between right and wrong.

This is known as the M’Naghten Test (sometimes spelled McNaghten or McNaughten). It is named after a 19th-century British defendant who attempted to kill a government official due to paranoid delusions the government was out to get him. He was found not guilty by reason of insanity because his mental illness rendered him incapable of understanding what he did was morally wrong.¹

If your mental state meets the McNaghten test, it does not matter whether it was a permanent condition or a temporary one—even if it lasted only a few hours. Temporary insanity qualifies for the California insanity defense just as a permanent mental condition does.²

Despite all this, the number of mentally ill criminal defendants who actually plead not guilty by reason of insanity is quite low. Nationwide, only about one percent (1%) of all criminal defendants assert the insanity defense.³

Example: Elizabeth suffers from severe depression, a debilitating mental illness. She shoplifts clothes from an expensive boutique and is arrested and charged with petty theft.

Elizabeth’s depression caused her not to care about the consequences of the shoplifting. But it did not prevent her from understanding what she was doing. It also did not prevent her from understanding that the theft was morally wrong.

So even though Elizabeth’s mental illness contributed to her criminal activity, she was not legally insane when she shoplifted—and so she cannot assert the legal defense of insanity.

California adopted the McNaghten rule as its definition of insanity when voters passed Proposition 8, known as the “Victim’s Bill of Rights,” in 1982. Remember, to win on an insanity defense, you only have to prove that either you were incapable of understanding the nature of your act or that you were incapable of distinguishing right from wrong: You do not have to prove both.

Example: Betty suffers from manic-depressive disorder. After filling up her gas tank, she drives away from the gas station without paying. A gas station attendant follows her on a motorcycle. Trying to escape him, Betty drives at over 80 mph and runs stoplights. Her reckless driving leads to an accident that kills another driver.

Betty is charged with vehicular manslaughter. She asserts the insanity defense. The jury decides that she WAS capable of understanding the nature of her actions—but was NOT capable of distinguishing right from wrong. Therefore, she is not guilty by reason of insanity.⁴

The Insanity Defense and Drug Addiction

Mental health problems and drug or alcohol addiction often go hand-in-hand. However, you may not claim insanity just because you were addicted to—or had recently used—drugs or alcohol when you committed the crime.

Example: Jeffrey suffers from acid flashbacks due to his earlier extensive use of the drug LSD. These flashbacks cause him to hear voices that aren’t really there. When he is at a bar, he mistakenly believes that the bartender is threatening him and attacks the man. This leads to him getting charged with California assault.

Because Jeffrey’s delusions were due to the use of drugs rather than a non-drug-related mental condition, he cannot assert the insanity defense.

However, if you were under the influence of drugs or alcohol when you committed a crime, the legal defenses of voluntary intoxication or involuntary intoxication may be of help to you.⁵ 

2. Proving Insanity

It is you the defendant—and not the prosecutor—who bears the “burden of proof” on the insanity defense.

In most aspects of a criminal trial, the prosecutor has the burden of proof. However, insanity in California is an affirmative defense, which means you admit to committing the crime but only because your conduct was excused.

So to win with the affirmative defense of insanity, you have the burden to prove that you were insane at the time of the crime and should therefore be excused from criminal liability.⁶

“Preponderance of the Evidence” Standard

If you plead the insanity defense in California, you must prove you were insane when the crime was committed by a “preponderance of the evidence. This means that you have to show that it is more likely than not that you were insane.

Contrast this to the “beyond a reasonable doubt” standard of proof that the prosecution has to meet when it comes to your guilt or innocence. “Beyond a reasonable doubt” means that the evidence is so strong that there is no logical explanation other than that you are guilty.

Note that under the preponderance of evidence standard, if the jury feels that neither side has the stronger argument on the insanity defense, then they must rule against you.⁷

3. The Plea

As discussed below, there are two ways to pursue an insanity defense in California. You can either:

1. Plead both “not guilty” and “not guilty by reason of insanity” or
2. Admit that you committed the crime but plead “not guilty by reason of insanity.”

1) Entering a “Dual” Plea

The first way to enter a California insanity plea is to enter two pleas – one of “not guilty,” and a second of “not guilty by reason of insanity.”

The first “not guilty” plea means that you did not actually commit the crime with which you were charged. The second plea means that you are asserting that—even if you did commit the crime—you should not be convicted because you were insane when you did so.

If you enter a dual plea, you will make your way through the California criminal court process as follows:

1. The first step will be a trial that covers the question of your guilt/innocence—not the question of your sanity;
2. If you are found not guilty, you go free, and the case is over; but
3. If you are found guilty at this stage, the case proceeds to a hearing on your sanity that is called the “sanity trial.” This hearing may involve the same jury who ruled on your guilt/innocence, or a new jury. In the sanity trial, the court will decide whether you should be found not guilty by reason of insanity.⁸

This process is what is called a “bifurcated trial”—because the question of your guilt and the question of your sanity are dealt with in two separate proceedings.

Sanity Hearings in California

During the sanity hearing, you or your attorneys present expert witnesses—usually psychiatrists—who testify that at the time of the offense, you either

1. Did not understand the nature of his/her act or
2. Did not understand that the act was wrong.²⁸

These are the only issues that are relevant during the sanity trial. If the jury decides unanimously that you were insane when you committed the crime, then you will be found not guilty by reason of insanity.

The sanity hearing usually takes place before a jury—but not always. A judge may remove the issue of insanity from the jury if they feel that you failed to present sufficient evidence that you were insane at the time of the crime.

Example: Victor is charged with aggravated California robbery. During his sanity hearing, he claims that he has suffered numerous blows to the head throughout his life—and that these have caused Satan to take over his body.

However, the two psychologists who examine Victor testify that they believe he is making that up. The prosecution also presents a recording of a conversation in jail in which Victor tells his brother that he is “doing the homeless nut routine.”

The judge therefore concludes that there is not enough evidence that Victor is actually insane—and does not let the jury consider his insanity defense.⁹

2) Entering a Single Plea

In some cases, you and your attorney may decide that it makes the most sense not to bother with a standard “not guilty” plea. Instead, you

• Concede that you are guilty of the offense and
• Only plead the insanity defense.

In these cases, the court proceeds directly to the sanity trial described directly above. There is no separate trial on guilt or innocence.¹⁰

4. Sentencing

If you successfully plead the insanity defense in California, then you will not receive the normal jail/prison sentence for your crime. Instead, you will be committed to a state mental hospital.

There are two reasons for commitment:

1. To rehabilitate and treat you and
2. To protect you and society from further harm.

You must remain in the state mental hospital until either:

1. Doctors believe that you regained sanity, or
2. The maximum term of imprisonment for that crime has expired, or
3. Doctors believe you would do well in an outpatient treatment program instead.¹¹

Frequently Asked Questions

What is the difference between the insanity defense and being “incompetent to stand trial”?

The insanity defense evaluates your mental state at the exact time the crime was committed. Incompetency to stand trial, on the other hand, evaluates your mental abilities at the time of your trial.

If a judge determines that a mental illness prevents you from understanding the court proceedings or assisting your attorney, the trial is paused, and you are sent for treatment until competency is restored. It is not a defense to the crime itself.

Can personality disorders, seizure disorders, or addiction be used to claim insanity?

California law explicitly states that personality disorders, adjustment disorders, seizure disorders, and addiction to (or abuse of) intoxicating substances cannot be the sole basis of an insanity claim. To successfully plead insanity, you must show additional evidence of a qualifying mental disease or defect, such as severe delusions or hallucinations.

What is the difference between temporary drug-induced psychosis and “settled insanity”?

While temporary insanity is a valid legal concept, it does not apply if you are simply experiencing a temporary, voluntary drug or alcohol-induced psychosis. However, courts recognize “settled insanity.”

Settled insanity occurs when long-term, chronic substance abuse (like chronic alcoholism or prolonged drug use) causes a permanent disease or defect of the mind. If this permanent defect leaves you legally insane even after the intoxicants have naturally left your system, you can assert an insanity defense.

Did California abolish the “diminished capacity” defense?

Yes. Under California Penal Code 25(a), the legislature explicitly abolished the “diminished capacity” defense. You can no longer argue that mental illness, trauma, or intoxication prevented you from having the capacity to form criminal intent in order to secure a complete acquittal.

As defense attorneys, we must now rely on formal insanity pleas or use mental health evidence to argue “diminished actuality” (showing you did not actually form the specific intent required for certain crimes).

If I know my actions were illegal, can I still be found legally insane?

Yes. The M’Naghten rule asks whether you understood the nature of the act or whether you could distinguish right from wrong. California case law (such as People v. Torres and People v. Coddington) clarifies that legal wrong and moral wrong are distinct.

Even if you knew an act was illegal, you can still be found insane if a severe delusion prevented you from understanding that the act was morally wrong (for example, a delusion that a higher power commanded the act to prevent a greater evil).

How does I get released from a state hospital after an insanity verdict?

A “not guilty by reason of insanity” (NGRI) verdict is not a permanent sentence. There are two primary pathways for release:

1. Conditional Release (CONREP): The hospital director can recommend supervised outpatient treatment if they believe you no longer pose a danger to the public.
2. Restoration of Sanity (Penal Code 1026.2): You can formally petition the court for a full restoration of sanity. After a mandatory year in an outpatient program, you have the right to a jury trial where you must prove, by a preponderance of the evidence, that you are no longer a danger to others. If successful, you are granted unconditional release.

Are there alternatives to pleading insanity if I am mentally ill?

Yes. Because the insanity defense is difficult to win and results in indefinite hospital commitment, you could instead seek Mental Health Diversion (Penal Code 1001.36). You may be eligible for this pre-trial diversion program if your mental disorder played a significant role in the charged offense.

If a judge grants diversion, prosecution is paused while you undergo mandated community-based treatment for up to two years. If treatment is successfully completed, the criminal charges are entirely dismissed.¹²

How does the insanity defense in Federal court differ from California state court?

If you are charged with a federal crime, you fall under the federal Insanity Defense Reform Act of 1984 rather than California’s Penal Code.

Federal law is much stricter: it requires the defense to prove severe mental disease or defect by “clear and convincing evidence.” This is a significantly higher burden of proof than California’s “preponderance of the evidence” (more likely than not) standard.

Additional Resources

For more in-depth information on the insanity defense, refer to the following scholarly articles:

• Mentally disordered offenders and the law: Research update on the insanity defense, 2004–2019 – International Journal of Law and Psychiatry.
• “The Angels That Surrounded My Cradle”: The History, Evolution, and Application of the Insanity Defense  – Buffalo Law Review.
  
• Not Guilty, Yet Continuously Confined: Reforming the Insanity Defense – American Criminal Law Review.
• Kahler v. Kansas: The End of the Insanity Defense? – Duke Journal of Constitutional Law and Public Policy.
• Sentencing Alternative to an Insanity Defense – Seattle Journal of Social Justice.

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