Not always, in fact it fails more often than it succeeds.
Some successful criminal defenses are used by the defense attorney to the accused and some defenses include: insanity, temporary insanity, and the non-guilty plea.
In an insanity defense, the defense must prove that the defendant is insane.
Voluntary intoxication or drug use is almost never the basis for the successful assertion of the insanity defense. However, in most states the defendant's intoxication or drug use may serve as the basis for a claim for diminished capacity.
Jnuary 1, 1996. Source: 8 Kan. J.L. & Pub. Pol'y 253 (1998-1999) Insanity Denied: Abolition of the Insanity Defense in Kansas; Rosen, Marc
Insanity defense and self defense
Voluntary intoxication or drug use is almost never the basis for the successful assertion of the insanity defense. However, in most states the defendant's intoxication or drug use may serve as the basis for a claim for diminished capacity.
As of 2021, four states have completely abolished the insanity defense: Idaho, Kansas, Montana, and Utah. These states do not allow defendants to plead not guilty by reason of insanity as a defense in criminal cases.
the Federal Insanity Defense Reform Act
0.25% of all cases.
Ingo Keilitz has written: 'The insanity defense and its alternatives' -- subject(s): Insanity, Jurisprudence
There are several differences but the main difference is a successful plea of insanity will, in most states, result in a verdict of "not guilty" and commission of the defendant to a mental institution. Diminished capacity merely results in the defendant being convicted of a lesser offense.
The insanity defense is alright as long as it is not used in just any case situation involving a murder. An insanity defense may allow a defendant who is mentally competent and has no history of mental illness to fake a specific mental disorder like Dissociative Identity Disorder (like in a Law & Order SVU episode titled "Alternate") and use it as a way to plead "not guilty by reason of insanity."