Cough syrup psychosis: Is it under-recognised?

To the Editor

Abuse of dextromethorphan (DM)-containing cough syrup formulations is becoming an increasing problem (Haroz and Greenberg, 2005). It is abused by adolescents, in particular, because of the euphoric effects; in addition, the drug is legal and relatively inexpensive. Acute mega-doses of the drug have profound psychological and physiological effects similar to those of phencyclidine (PCP), another N-methyl d-aspartate (NMDA) antagonist (Schwartz, 2005).

Mr Z is a 22-year-old male who presented initially at the age of 19 with a cannabis-induced psychotic episode. He then presented subsequently on numerous occasions with psychotic symptoms and a negative urine drug screen. He was maintained on antipsychotic therapy and diagnosed with a schizoaffective disorder.

It was not until a recent presentation where empty bottles of cough syrup formulation Robitussin were located in his room that Mr Z admitted to first consuming Robitussin in excess at the age of 18, and abusing it intermittently since. Ongoing abuse of Robitussin during this admission was resulting in continual episodic deterioration. Mr Z would take 600 mg, which is greater than 20 times the recommended dose.

In total, Mr Z had nine admissions to hospital. These presentations were later reformulated as likely being attributable to DM abuse in the context of an underlying vulnerability to psychosis. There was no hereditary predisposition.

Mr Z reported that he enjoyed an initial euphoria and sense of dissociation, with onset soon after consumption. This was then followed by psychotic symptoms, which on average lasted 2 weeks, demonstrating no clear response to antipsychotic medication and often requiring closed-ward management. During the psychosis Mr Z described visual hallucinations – ‘shadows’, auditory hallucinations, paranoia and irritability. Objectively he was reported to appear flushed and display disorganised and intrusive behaviour, poor self-care and fatuous incongruous affect, often pacing the ward corridors and responding to internal stimuli. After his psychotic symptoms resolved he maintained remission until he took DM again.

PCP is known to induce psychosis through noncompetitive antagonism of NMDA-type glutamate receptors (Javitt, 2012). DM has the same mechanism of action, which accounts for the neurobiological plausibility of the development of psychotic symptoms (Stahl, 2007). There have been previous reports of DM-induced psychosis (Price and Lebel, 2000). The specific mechanisms by which this occurs are still contentious. There are a number of hypotheses that currently exist, including downstream effects on dopamine regulation, resultant glutamate excess in the prefrontal cortex and down-regulation of parvalbumin expression in GABAergic interneurons (Stahl, 2007, Javitt, 2012). The lack of a clear response to antipsychotic medication in the case described suggests an alternate mechanism than that mediated purely by dopamine.

As medical practitioners we should now be aware of the growing incidence of the abuse of cough syrup preparations (Haroz and Greenberg, 2005) and the potential for associated psychiatric consequences. DM abuse should be considered in atypical presentations of psychosis, particularly in young people, such as the case presented, in which there was an element of delirium, symptoms did not resolve as rapidly as usual and response to antipsychotic medication was not observed.