What If I Didn’t Know What I Was Doing? The Legal Difference Between Intoxication and Mental Illness in NSW..

You’ve been charged with assault, a breach of an AVO, or another serious offence — but you genuinely don’t remember what happened. Maybe you were intoxicated. Maybe you were in a state of mental confusion, panic, or psychosis. Either way, you’re wondering:

“If I didn’t know what I was doing, can I still be found guilty?”

In NSW, the law draws a clear legal line between mental illness and intoxication. One may offer a complete legal defence. The other — almost never. And even reductions are rare..

At National Criminal Lawyers®, we regularly represent clients in drug-related violence, domestic disputes, and mental health matters where this issue is critical. Understanding the legal difference is key to building the right defence and getting the right outcome.

 

Mental Illness — A Recognised Defence

Under section 28 of the Mental Health and Cognitive Impairment Forensic Provisions Act 2020 (NSW), a person is not criminally responsible for an offence if:

• They had a mental health or cognitive impairment at the time of the offence; and
  
  
• This prevented them from understanding the nature or wrongness of their actions.
  
  

This is the classic McNaghten rule, and if accepted, it leads to a verdict of “not guilty by reason of mental illness.”

 

 

Intoxication — A rare defence, often mitigatory at best..

1. Intoxication Defence for Specific Intent Offences — But Only in Limited Situations

Under section 428C(1) of the Crimes Act 1900 (NSW), intoxication — even if self-induced — may be considered when determining whether the accused had the specific intent required to commit certain serious offences. These specific intent offences include:

• Murder (intent to kill or cause grievous bodily harm)
  
  
• Wounding with intent
  
  
• Intentionally causing grievous bodily harm (GBM)
  
  
• Intentionally damaging property
  
  

For example, if a person commits an act that would ordinarily amount to murder but was so intoxicated they could not form the intent to kill, they may avoid a murder conviction and instead be found guilty of manslaughter.

However, this defence is NOT available if:

• The accused already intended to commit the offence before becoming intoxicated; or
  
  
• The intoxication was deliberately induced to facilitate the offence (s 428C(2)).
  
  

In these cases, intoxication cannot negate intent.

2. Involuntary Intoxication as a Defence for Any Offence

Under section 428D(b), involuntary intoxication — where the accused did not voluntarily consume the intoxicating substance — can be considered for any criminal offence, not just specific intent crimes.

Examples include:

• Being drink-spiked
  
  
• Drugged without consent
  
  
• Taking a mislabelled or unknown intoxicating substance
  
  

In such scenarios, the defence can argue that the accused:

• Did not form the necessary intent
  
  
• Did not understand their actions
  
  
• Lacked the capacity to commit the offence
  
  

This defence is rare but important when applicable.

 

When Can Intoxication NOT Be Used as a Defence?

For general intent offences — such as common assault, sexual assault, breaching an apprehended violence order (AVO), or resisting police — self-induced intoxication cannot be used to deny the mental element of the offence (s 428D(a)).

For example, if someone gets drunk and assaults another during a fight, they cannot claim intoxication to excuse the assault.

 

Can Intoxication Still Influence Sentencing?

While intoxication may not always provide a full defence, it can be a mitigating factor during sentencing, especially when linked to broader issues like addiction, mental illness, trauma, or PTSD. Courts will consider:

• Whether the offender has shown insight or engaged in treatment
  
  
• If the conduct was impulsive and not premeditated
  
  
• Evidence of rehabilitation
  
  
• The offender’s character
  
  

The Verdins principles guide courts in assessing how addiction or mental illness may reduce moral culpability.

However, courts are less sympathetic if the offender has:

• Multiple offences involving intoxication
  
  
• Made no effort to address substance abuse
  
  

Key Distinction: Capacity vs Consequence

Factor	Mental Illness	Intoxication
Is it a legal defence?	Yes	Not usually
Can it negate criminal intent?	Yes, if proven under s 28	Not if self-induced
Can it be self-inflicted?	Yes	Not a defence if voluntarily induced
How courts treat it	As a possible complete defence	As a personal responsibility issue
Can it impact sentencing?	Often reduces culpability	Sometimes (if linked to trauma/addiction)

Case Example: Mental Illness vs Intoxication in Practice

Case 1 – Intoxication:
 Jason attends a party, consumes MDMA and alcohol, and later assaults a stranger. He claims he doesn’t remember what happened.

Result: The court finds him criminally responsible. Voluntary intoxication is not a defence. He may receive some leniency at sentencing if linked to addiction, but not acquittal.

Case 2 – Mental Illness:
 Sarah, diagnosed with schizophrenia, experiences a psychotic episode and breaches an AVO by visiting her ex-partner’s home. She believes she’s following a divine instruction.

Result: With expert psychiatric evidence, Sarah may be found not guilty by reason of mental illness and referred to the Mental Health Review Tribunal, not prison.

What About Drug-Induced Psychosis?

A key case that helps clarify how courts treat drug-induced psychosis is R v Meddings [1966] VR 306. In that case, the court held that a psychotic state brought on by voluntary drug use is not a “disease of the mind”, and therefore doesn’t qualify for the mental illness defence.

This remains a guiding principle today — if the psychosis is caused solely by self-induced intoxication, it’s treated as intoxication, not mental impairment.

Thus, whether it can be used as a defence of a mitigating factor aligns closely intoxication, as previously covered:

• If the psychosis results from voluntary drug use, it’s generally excluded as a defence, especially for general intent offences.
  
  
• It may only be considered for specific intent offences — and even then, only if the person didn’t already plan the crime before becoming intoxicated (s 428C).
  
  
• It might assist at sentencing if linked to an underlying condition and there’s evidence of rehabilitation — but not if it’s repeated or habitual.

Frequently Asked Questions

Can I use both intoxication and mental illness in my defence?

Possibly — but only if your mental illness existed outside of your intoxication. Courts will not accept intoxication as a shield unless it can be clearly separated from the mental impairment.

What if I didn’t intend to commit the act?

Intent is crucial in many offences — but intoxication won’t help you avoid liability for intent if you drank or used voluntarily. Mental illness may negate intent only if it impaired your understanding of the act’s wrongness.

Summary: What the Law Actually Allows

• Mental illness can be a complete defence if it stops you from understanding what you’re doing or that it was wrong.
• Intoxication, if self-induced, is ONLY a defence for specific intent offences

If you genuinely did not understand your actions due to mental illness, that may be a legal defence — but you’ll need expert support, reports, and experienced criminal lawyers to make the argument effectively, such as us — the top criminal defence lawyers Sydney.

Call National Criminal Lawyers® Today

Facing charges where mental illness, intoxication, or psychosis played a role?

📞 Call 1800 CRIM LAW today for a free first consultation.

We offer:

• Fixed fees
  
  
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• Offices in Sydney, Parramatta and Greater NSW
  
  

We know how to separate excuses from defences — and we fight to protect the ones that count.