My question was prompted by an episode of the TV show Arrow. The subject of my question is the law not science fiction so I won't go into too much detail, but a character is killed and resurrected by a Lazarus pit, which has the side effect of blood lust, the involuntary and uncontrollable urge to kill. That being said, imagine a more realistic scenario where a person is unwillingly dosed with a drug that induced the same uncontrollable rage and fear causing this person to unknowingly kill an innocent person that in fact posed no threat. Could psychological impairment be a full defense for the murder, in that they are found not guilty as they had no control over their actions?

  • 2
    The novel and movie Anatomy Of A Murder (based closely on a real-life case) centres on the defence of irresistible impulse, which seems to match the question.
    – gidds
    Oct 8, 2023 at 10:17
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    Hopefully the prosecutor believes that the situation is as described and simply doesn’t prosecute. The person to be prosecuted is the drug-administrator.
    – jmoreno
    Oct 8, 2023 at 15:48

2 Answers 2


The criminal code has sections 20 and 21, Lack of criminal responsibility due to mental disorder and Diminished responsibility here

Whoever, at the time of the commission of the offence, is incapable of appreciating the unlawfulness of their actions or of acting in accordance with any such appreciation due to a pathological mental disorder, a profound disturbance of consciousness or intellectual disability or any other serious mental disorder is deemed to act without guilt.

If the offender’s capacity to appreciate the unlawfulness of the act or to act in accordance with any such appreciation is substantially diminished at the time of the commission of the offense due to one of the reasons indicated in section 20, the penalty may be mitigated pursuant to section 49 (1).

So yes, a scenario like yours is possible and may result in acquittal, and actually, there are many cases where the offender was intoxicated by alcohol and gets a (slightly) less severe sentence. Voluntary intoxication by other drugs won't help you much as consuming those drugs is an offense in itself, and there is also section 323a which handles willful intoxication in order to be elegible for sections 20/21.

Being acquitted under section 20 is not always in the interest of the offender, though, because if they are still deemed a threat to the public, they will be admitted to a mental hospital and kept there until they are not a threat any more. This typically means a yearly examination, and the patient can fail this examination again and again, resulting in what's not officially imprisonment but without much difference to the patient, eventually for an even longer time than a prison sentence would have been, and especially the offender won't know when, if ever, they will be free again.



In the scenario you describe, the person has "no control over their actions." This brings it squarely within the definition of "automatism" in Canadian law.

Conduct that is truly involuntary (in the sense that the person is in a "state of impaired consciousness... in which [they have] no voluntary control over [their] action") cannot be criminal (R. v. Brown, 2022 SCC 18, para. 2).

A person in a state of automatism is "incapable of voluntarily committing a guilty act or of having a guilty mind" (Brown, para. 6).

It would be an infringement of ss. 7 (right to life, liberty, and security of the person and the right not to be deprived thereof except in accordance with the principles of fundamental justice) and 11(d) (right to be presumed innocent...) of the Canadian Charter of Rights and Freedoms to criminally punish a person for acts taken in such circustances (Brown, para. 9).

Not criminally responsible on account of mental disorder (NCRMD)

Section 16 of the Criminal Code also sets out a defence for any act or omission, including homicides, where the act was commited or omission made "while suffering from a mental disorder that rendered the person incapable of appreciating the nature and quality of the act or omission or of knowing that it was wrong."

The party seeking to establish the claim of NCRMD must establish that the accused:

  1. was suffering from a mental disorder; and

    2a. was unable to appreciate the nature and quality of the act; or

    2b. did not know it was wrong (in the moral sense, not legal sense).

The fact that the person in your scenario would "unknowingly kill" seems to go a significant way to establishing element 2a. The only remaining element to establish would be that the person was suffering from a mental disorder at the time of the act. This has been defined to be a "disease of the mind" which embraces "any illness, disorder or abnormal condition which impairs the human mind and its functioning, excluding however, self-induced states caused by alcohol or drugs, as well as transitory mental states such as hysteria or concussion" (R. v. Cooper (1979), [1980] 1 SCR 1149).

Selection of a defence

If both defences are open to the accused, they would likely attempt to establish the plain (non-mental-disorder) automatism defence rather than NCRMD. A finding of NCRMD risks placing the accused in custody in hospital under the supervision of the Review Board. Non-mental-disorder automatism on the other hand would result in an unqualified acquittal.

However, even if the accused attempt to proceed by defence of automatism, the Crown may attempt to show that it is mental-disorder automatism (or some non-automatism-based NCRMD claim).

mental disorder automatism is subsumed by the defence of mental disorder as set out in the Code.Accordingly, a successful defence of mental disorder automatism will result in a verdict of not criminally responsible on account of mental disorder as dictated by s. 672.34 of the Code. Under s. 672.54, an accused who receives this qualified acquittal may be discharged absolutely, discharged conditionally or detained in a hospital. In contrast, a successful defence of non-mental disorder automatism will always result in an absolute acquittal.

(R. v. Stone, [1999] 2 SCR 290)

The analysis is two-stage (R. v. Stone, [1999] 2 SCR 290):

  1. The accused would attempt to establish automatism.
  2. If the condition alleged by the party seeking to establish NCRMD is in fact a "mental disorder," the trier of fact would be asked to also decide between mental-disorder automatism or non-mental-disorder automatism.

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