Journal of Addiction Research & Therapy
Open Access

Legislation defining criminal responsibility in the presence of serious psychiatric disorders does not usually specifically address how this should be understood where the mind of the accused may have been influenced by their use of drugs [1]. While that may not be a significant problem where the drug involved is alcohol, because of well-established legal precedents in many countries, it is a major emerging issue with illicit drug use and most particularly with methamphetamine [2]. Probably also potentially with cannabis and cannabinoids [3-5]. The evidence given by expert witnesses in such cases usually centre on the concept of substance induced psychosis, confusing that with “intoxication." Some jurisdictions have ruled against such cases having a NGRI (Not Guilty by reason of Insanity) defence on the grounds that the “Disease of the Mind” was a consequence of an external agent. No comprehensive list of argued cases is known to the author, but a recent sample of one forensic psychiatrists last 10 years of contested case shows drug related psychoses to be relatively common events [6].

The accepted classifications of psychiatric disorders define most of them as syndromes by their phenomenology, without causal implication [7]. For example it is now clear that schizophrenia is a syndrome with probably many different, individually minor, pathogenic contributors, those varying from person to person [8].

It has been recognized for more than 50 years that amphetamines can produce a mental state which contains the phenomenological elements of schizophrenia. The ability of some illicit drugs, particularly methamphetamine, to produce a disorder which also mimics schizophrenia in its course and chronicity has only become clear in this millennium despite being raised in the Lancet more than 30 years ago [3,4,9,10]. Accordingly, we now know that some persons with schizophrenia suffer from it because of the extent of their methamphetamine use. There is a relationship between the quantified (frequency and dose) exposure and the enhanced risk of enduring psychosis [11]. This parallels medicines understanding of many conditions (e.g., melanoma, lung cancer, mature onset diabetes) where the diseases are diagnosed long after causal exposure. Heavy methamphetamine users thus show an increased rate of the psychiatric disorder, schizophrenia, which most commonly underpins a legal defense of NGRI (not guilty by reason of insanity) [12].

Accused persons diagnosed as suffering from schizophrenia in the context of repeated and heavy dosage methamphetamine and who seek an NGRI verdict usually argue that they do not have a drug induced psychosis if the psychosis continues after the drug has been eliminated from their body. This can now be seen to be literally incorrect [3,10]. Legal precedent and sometimes forensic psychiatrists without the benefit of current psychiatric knowledge are confused on the same issue [4].

Legislators and the Courts need to make it clear whether or not they will accept schizophrenia as a “Disease of the Mind” as that term is used in countries whose relevant legislation dates back to the M’Nagten rules [12] regardless of its cause or pathogenesis. Or that they regard drug induced conditions as excluding a NGRI verdict, on the grounds that the “users” took the drugs in the knowledge that they might reduce judgement or influence motivation, which is sometimes considered to be the underlying reason for intoxication with alcohol to not reduce culpability [5].

In democracies the laws are generally considered to serve the populations needs and wishes. So legislations evolve over time, perhaps in recent centuries reflecting, for example, increasing efforts to both subserve the needs of communities, increase recognition of individuals rights and societal movements towards humanitarianism. In that context, most countries legislative underpinning of NGRI reflect the societal setting of the 1840s [1], which long antedate current patterns of illicit drug use and societal attitudes. It would therefore appear timely for those countries whose relevant legislations date back to 1843 to now formulate laws which reflect twenty-first century societal values and psychopharmacologic knowledge. Do countries wish to anchor their “mens rea” views on the cause of the psychosis (i.e., drug induced) or the timing (e.g., intoxication) of the relevant chemical ingestion?