Drug Addiction and Crime in Japan: How Does Substance Abuse Impact Criminal Responsibility?

Japanese Attorney at Law - Bengoshi L.L.

02 Jun 2025 • 11 min read

The relationship between drug addiction, substance abuse, and criminal behavior is a complex issue that legal systems around the world grapple with. In Japan, when an offense is committed by an individual suffering from drug addiction (薬物中毒 - yakubutsu chūdoku) or while acutely under the influence of drugs, a critical question arises: how does their state of mind, altered by substance abuse, affect their criminal responsibility (刑事責任能力 - keiji sekinin nōryoku)? Japanese criminal law provides a framework for this assessment, but its application is nuanced, often involving intricate psychiatric evaluations and a careful weighing of various factors.

This article delves into how the Japanese legal system evaluates criminal capacity in cases involving drug use, focusing on the governing legal principles, the pivotal role of psychiatric evidence, and the insights gleaned from a significant Tokyo High Court decision involving crimes committed under the influence of stimulants.

The General Legal Framework: Article 39 of the Penal Code and the Principle of Intoxication

The primary legal provision governing criminal responsibility in relation to mental state is Article 39 of the Japanese Penal Code. It stipulates:

Article 39, paragraph 1 (Legal Insanity - 心神喪失, shinshin sōshitsu): "An act of a person who is in a state of insanity is not punishable." This leads to an acquittal.
Article 39, paragraph 2 (Diminished Capacity - 心神耗弱, shinshin kōjaku): "Punishment shall be reduced for an act of a person whose capacity is diminished." This results in a mandatory reduction of the applicable sentence.

The prevailing legal test for these states is the "biological-psychological mixed method" (混合的方法 - kongōteki hōhō), which requires both:

A biological element: The presence of a "mental disorder" (精神の障害 - seishin no shōgai).
A psychological element: As a result of this disorder, the person lacked (for insanity) or had significantly impaired (for diminished capacity) the ability to discern the wrongfulness of their conduct (辨識能力 - benshiki nōryoku) or to act in accordance with that discernment (制御能力 - seigyo nōryoku).

Voluntary Intoxication and Actio Libera in Causa

As a general rule, voluntary intoxication by alcohol or drugs does not, in itself, negate or diminish criminal responsibility in Japan. This principle is reinforced by the doctrine of actio libera in causa (原因において自由な行為 - gen'in ni oite jiyū na kōi – an act free in its cause). If an individual voluntarily and culpably (intentionally or negligently) consumes substances knowing they might become incapacitated and commit a crime, they can generally be held fully responsible for actions committed while in that intoxicated state. The culpability lies in the act of self-intoxication with foresight of potential criminal conduct.

When Can Drug Use Impact Legal Capacity?

The question of criminal responsibility becomes more complex when drug use is not merely recreational or a single instance of voluntary intoxication but leads to a recognized "mental disorder" that profoundly impairs the psychological capacities relevant to Article 39. Such situations can arise from:

Acute Intoxication: The immediate, overwhelming effects of certain drugs can sometimes induce a temporary psychotic state or such a severe impairment of cognitive and volitional faculties that it meets the criteria for diminished capacity or, rarely, insanity.
Chronic Addiction and Drug-Induced Mental Disorders: Long-term, severe drug addiction can lead to more persistent mental health conditions, such as drug-induced psychosis (e.g., stimulant psychosis), lasting cognitive impairments, or severe personality changes that exist at the time of the offense and significantly impact the defendant's mental capacity.

Stimulant Psychosis and Other Drug-Induced Mental States

In Japan, stimulant (覚せい剤 - kakuseizai), particularly methamphetamine, abuse is a significant concern and frequently figures in cases where drug-induced mental states are at issue. Chronic or high-dose stimulant use can lead to:

Stimulant Psychosis (覚せい剤精神病 - kakuseizai seishinbyō): This condition is often characterized by prominent psychotic symptoms, including:
- Delusions: Commonly persecutory (e.g., believing one is being watched, followed, or plotted against) or referential (misinterpreting ordinary events as having special personal meaning).
- Hallucinations: Primarily auditory (hearing voices) but can also be visual or tactile.
- Paranoia and Suspiciousness: An intense and pervasive distrust of others.
- Agitation and Irritability: Heightened emotional reactivity and potential for aggression.
  The symptoms of stimulant psychosis can strikingly resemble those of paranoid schizophrenia, making careful psychiatric differentiation crucial.
Flashbacks (フラッシュバック現象 - furasshubakku genshō): Some individuals may experience spontaneous recurrences of drug-induced perceptual distortions or psychotic symptoms even during periods of abstinence.
Severe Withdrawal Symptoms: While typically associated with physical distress, withdrawal from certain drugs can also involve significant psychological disturbances that might, in extreme cases, affect behavior and judgment.
Long-Term Cognitive Impairment: Chronic substance abuse can lead to more enduring deficits in areas such as executive function, impulse control, memory, and judgment, which could be relevant to understanding the defendant's overall mental functioning.

A mere diagnosis of drug addiction or evidence of being under the influence of drugs at the time of an offense does not automatically translate into a finding of legal insanity or diminished capacity. Japanese courts undertake a highly individualized, case-by-case analysis, often referred to as a "comprehensive judgment" (総合的判断 - sōgōteki handan).

The core of this inquiry is the nexus between the drug-induced mental state and the defendant's legally relevant capacities (discernment and control) at the specific time the crime was committed.

Forensic psychiatrists in Japan have debated the appropriate legal treatment of conditions like stimulant psychosis. Some have argued that its profound impact on reality perception and thought processes warrants a finding of irresponsibility similar to that in cases of schizophrenia. Others contend that even within a psychotic state induced by stimulants, the individual's core personality and some degree of ego function might remain more intact than is typically seen in schizophrenia, suggesting that some capacity for judgment or control may be retained.

The prevailing judicial approach in Japan has tended towards the more cautious latter view. Courts meticulously examine the totality of the evidence, including:

The defendant's history and pattern of drug use.
The nature and severity of any psychiatric symptoms (delusions, hallucinations, etc.) present at the time of the offense.
The defendant's observable conduct before, during, and after the crime.
The relationship between the symptoms and the criminal act itself (e.g., was the act a direct product of a specific delusion?).
The defendant's underlying "original personality" (元来の人格 - ganrai no jinkaku) and whether the crime represents a complete break from it or an exaggeration of pre-existing traits.

Key Case: The Gang Member's Stimulant-Fueled Rampage (Tokyo High Court Decision, November 27, 1984)

The Tokyo High Court decision of November 27, 1984 (Tōkyō Kōtō Saibansho Hanketsu, Shōwa 59-nen 11-gatsu 27-nichi, Hanrei Jihō 1158-gō 249-ページ) provides a classic illustration of this judicial approach.

Factual Background

The defendant was a member of an organized crime group (暴力団 - bōryokudan) with a history of stimulant (kakuseizai) abuse. At the time of the offenses, he was suffering from significant effects of stimulant use, including hallucinations and delusions. These included intense jealous delusions concerning his cohabiting partner ("A") and a junior gang member ("E"), as well as persecutory delusions (e.g., believing he was being pursued by police after he had earlier assaulted A due to his jealousy).

Under the influence of this drug-induced mental state, the defendant committed a series of serious crimes:

He assaulted his partner A, driven by jealous delusions.
Believing the police were after him for this assault, he fled.
In an attempt to find A, he located A's sister and, to coerce information about A's whereabouts, threatened her. He then abducted A's sister, forcing her into his car.
During a prolonged period of driving to evade both real and perceived police pursuit, with A's sister still captive:
- He stopped at a gas station and fired his shotgun to threaten an employee.
- He fired the shotgun at a pursuing police car.
- Ultimately, during a standoff, he shot and killed a police officer who was attempting to de-escalate the situation and persuade him to surrender.

The defendant was also charged with illegal possession of the shotgun and ammunition, use and possession of stimulants, and driving without a license.

Conflicting Psychiatric Evaluations

The case involved conflicting psychiatric opinions regarding the defendant's mental state and responsibility:

An initial psychiatric evaluation conducted during the investigation stage downplayed the direct influence of stimulants as the primary cause of his actions and concluded that he possessed full criminal responsibility.
Subsequent psychiatric evaluations presented during the trial and appeal stages (by different experts) took a different view. These experts concluded that the defendant's series of offenses were committed while he was suffering from stimulant-induced psychosis, characterized by active hallucinations and delusions. They opined that this psychotic state was so severe as to suggest legal insanity.

Court Rulings

The first instance court (District Court) sided with the initial psychiatric evaluation and found the defendant to have full criminal responsibility for all charges.
The Tokyo High Court, on appeal, reached a different conclusion. It found the defendant to have been in a state of diminished capacity (shinshin kōjaku). Its reasoning was detailed:Based on this comprehensive analysis, the Tokyo High Court concluded that while the defendant's capacity to discern wrongfulness and to control his actions was significantly impaired by the stimulant-induced psychosis, these capacities were not entirely extinguished. Thus, a finding of diminished capacity was deemed appropriate.
1. Acknowledgement of Stimulant Psychosis: The High Court accepted the trial-stage psychiatric evidence that the defendant was indeed suffering from an abnormal mental state due to stimulant use, experiencing significant delusions and hallucinations at the time he committed the crimes.
2. Psychosis Did Not Wholly Dominate Personality: However, the High Court determined that the defendant's personality and cognitive functions were not completely overwhelmed or dominated by these psychotic symptoms. Several observations supported this crucial distinction:
  - Preserved Cognitive and Volitional Abilities: Despite his psychotic state, the defendant demonstrated an ability to understand the meaning and (to some extent) the unlawfulness of his actions. He also exhibited goal-directed behavior and a degree of self-control. For example, his efforts to evade police, his abduction of A's sister as a means to find A, and his tactical (though criminal) use of the shotgun to threaten and later to kill, all suggested a level of retained cognitive functioning and purposeful action.
  - Link to Underlying ("Original") Personality Traits: The High Court considered the defendant's pre-existing personality. He was described as having traits such as being inherently suspicious, prone to holding grudges, easily angered, and quick to resort to violence even when not acutely psychotic. The Court found that his criminal actions, while undeniably influenced and exacerbated by the stimulant psychosis, were also, in part, an expression or an extreme manifestation of these underlying personality characteristics. The crimes were not seen as entirely alien to his "original personality" (heiso towa mattaku kotonaru sakuran jōtai ni okeru kōdō towa mitomerarenai – his actions were not recognized as those of someone in a state of confusion completely different from his usual self).
  - Delusions Not Always the Sole or Direct Motivator: While his jealous and persecutory delusions clearly fueled his initial actions and overall paranoid state, the High Court found that these delusions were not necessarily the sole and direct cause of every criminal act. For instance, the fatal shooting of the police officer was reportedly triggered by the defendant misinterpreting the officer's attempt at a reassuring smile as a sign of mockery or confidence in an easy arrest. This, while occurring within a paranoid delusional framework, still involved a degree of situational (mis)interpretation and a decision-making process by the defendant's "ego" (jiga), however distorted.

Significance of the 1984 High Court Case

This detailed High Court ruling is highly illustrative of the Japanese judiciary's typical approach in cases involving stimulant psychosis:

Diminished Capacity More Common than Insanity: It exemplifies a common trend where stimulant-induced psychosis leads to a finding of diminished capacity rather than full legal insanity.
"Illness vs. Original Personality" Analysis: The case strongly highlights the judicial practice of examining the interplay between the acute effects of the drug-induced mental disorder and the defendant's underlying, pre-existing personality traits and behavioral tendencies. The court tries to discern how much of the criminal conduct is attributable to the direct impact of the psychosis and how much stems from the individual's character, albeit possibly disinhibited or distorted by the drug's effects.
Retained Ego Functions: It underscores that if there is evidence of retained ego functions—such as goal-directed behavior, some level of situational awareness (even if misinterpreted), or actions that align with pre-existing personality patterns—courts are generally hesitant to conclude a complete lack of criminal responsibility, even in the presence of clear psychotic symptoms like delusions and hallucinations.

Drawing from the principles applied in the 1984 Tokyo High Court case and general Japanese forensic practice, courts undertake a "comprehensive judgment" (sōgōteki handan) by considering a wide array of factors:

History and Pattern of Drug Use: This includes the type of drug(s) used, the duration and frequency of use (chronic versus acute), dosage levels, and any history of prior drug-related psychiatric episodes.
Nature and Severity of Psychiatric Symptoms at the Time of the Offense: The specific type, intensity, and pervasiveness of any delusions, hallucinations, disorganized thought, or other psychotic symptoms are meticulously examined.
Defendant's Observable Conduct: This involves analyzing the defendant's actions before, during, and after the crime. Was there evidence of planning, or was the act impulsive and disorganized? How coherent were their actions? Did they show awareness of their surroundings? Were there attempts to evade capture, conceal evidence, or protect themselves?
Relationship Between Symptoms and the Crime: A crucial aspect is determining the directness of the link between the psychiatric symptoms and the criminal act. For example, was the crime a direct and understandable (from the perspective of the delusional system) response to a specific delusion or command hallucination? Or were the symptoms a more general backdrop to actions that might have also been driven by other, non-psychotic motives (e.g., anger, greed, revenge)?
Defendant's "Original Personality" and Typical Behavior: Courts often try to understand the defendant's personality traits and behavioral patterns as they existed before the onset of severe drug-induced problems or the acute psychotic episode. Does the criminal act represent a complete and bizarre departure from their known sober personality, or is it, to some extent, an exaggeration or disinhibition of pre-existing tendencies (such as impulsivity, aggression, poor judgment, or anti-social attitudes)?
Memory of the Offense: While amnesia for the event can be a feature of some drug-induced states (and also of some genuine psychotic episodes), its presence or absence is not conclusive. Detailed memory might suggest a certain level of conscious awareness, but feigned amnesia is also a possibility.
Insight into Illness and the Effects of Drugs: Did the defendant have any awareness that they were suffering from a drug problem, that they were under the influence, or that their perceptions might be distorted by drugs?
Expert Psychiatric Opinion: The findings and reasoning of psychiatric experts are given considerable weight, especially concerning the diagnosis and the nature of the symptoms, but, as noted, the ultimate legal conclusion on capacity remains with the court.

Considerations for Other Types of Drugs

While stimulant-related offenses are a prominent concern in Japan, the general principles of capacity assessment apply to crimes committed under the influence of other psychoactive substances as well, such as organic solvents (シンナー - shinnā – often abused through inhalation), cannabis, hallucinogens, opioids, or the ever-evolving array of synthetic ("designer" or "dangerous") drugs (脱法ドラッグ - dappō doraggu). The specific psychoactive effects of each particular drug, its typical impact on perception, cognition, and volition, and its known potential to induce psychotic states or severe impairment will be critical factors in the psychiatric and legal evaluation. The challenge for the courts can sometimes be the lack of extensive forensic psychiatric literature or experience with newer or less commonly abused substances.

Conclusion

Japanese criminal law approaches the issue of criminal responsibility in drug addiction and drug intoxication cases with a degree of nuance. While voluntary intoxication, as a general rule, does not excuse criminal conduct, the law recognizes that severe drug abuse can lead to qualifying mental disorders, such as stimulant-induced psychosis, which may significantly impair an individual's capacity for discernment or control at the time of an offense.

In such cases, a finding of diminished capacity is more common than one of full legal insanity. The judiciary, as exemplified by the 1984 Tokyo High Court decision, undertakes a comprehensive assessment. This involves not only evaluating the direct impact of drug-induced symptoms like delusions and hallucinations but also carefully considering the extent to which the defendant's "original personality" and retained cognitive or volitional functions contributed to the criminal act. The ultimate determination is a fact-intensive legal judgment, guided by expert psychiatric evidence, that seeks to ascertain whether the defendant, at the moment of the crime, possessed the fundamental mental capacities required for criminal culpability. This balanced approach reflects the ongoing effort to reconcile principles of individual responsibility with an understanding of the profound impact that severe substance abuse and addiction can have on the human mind.