Misuse and dependence of dimenhydrinate: A mixed studies systematic review.

BACKGROUND: Dimenhydrinate (DMH) is an antihistamine used to treat nausea and vomiting. Although widely available in pharmacies as an over the counter medication, there have been reports of potential DMH tolerance and dependence and a possible euphoric potential accompanying heavy use (>100 mg/day). Despite the potential for misuse, there is a gap in the literature concerning patterns, characteristics, and potential mechanisms of DMH misuse.

AIMS: This review aimed to synthesize evidence on the pharmacology, clinical effects, and management of DMH misuse and dependence to inform clinical decision making and relevant drug policy.

METHODS: We conducted a systematic review in accordance with the PRISMA guidelines and using Cochrane collaboration methods. We searched seven databases from their inception through July 2019. To be included in the review, studies needed to measure or focus on one or more dimensions of morbidity or mortality related to the misuse of DMH. Quantitative, qualitative and mixed-method studies were included in order to capture the breadth of possible studies. Studies were excluded if they did not fit into the conceptual framework of the study of if they focused primarily on the misuse of other substances. A narrative synthesis of study findings was pursued given the limited capacity for a quantitative meta-analysis.

FINDINGS: We identified 24 studies, which described a range of neuropsychiatric sequelae related to DMH consumption, including seizures, psychosis, depression, intoxication (resembling anticholinergic syndrome) and withdrawal. The sedative and euphoric properties, readily available nature, and low cost of DMH appear to facilitate DMH dependence, which were more commonly reported among individuals who had concurrent psychiatric disorders, displaying symptoms such as low motivation, poor concentration, and delirium. The overall quality of studies identified by this review was low-largely because the majority of studies were case reports or review articles, with few intervention or cohort studies.

CONCLUSIONS: There is some evidence to suggest the existence of DMH-related syndromes involving intoxication, withdrawal, and dependence, more commonly among long-term, heavy DMH consumers. However, higher quality studies are needed to confirm preliminary findings that there may be a biological basis for such syndromes.