Misuse of over the counter and prescription only medication by people accessing specialist treatment services: a systematic review
Authors: Gittins R E , Missen Louise L , Maidment I 
Published: April 2022

Abstract

Introduction
Over the Counter (OTC) and Prescription Only Medication (POM) are misused by people who access substance misuse services (SMS). Harms include impact upon physical/mental wellbeing and potentially fatal overdoses, with concerns growing amongst healthcare professionals, commissioners and the general public (1). SMS must respond to increasing demand and no known systematic review has explored this (2).

Aim
To examine the literature on the pattern of OTC/POM misuse among adults accessing SMS, including the types of medication, prevalence and associated characteristics.

Methods
The protocol for this systematic review has been published (2), registered on PROSPERO (CRD42020135216) and undertaken in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). A comprehensive search was conducted, incorporating Cochrane, OVID Medline, Pubmed, Scopus and Web of Science databases and grey literature. Two independent reviewers conducted the title and abstract screenings, followed by full-text reviews, using predetermined selection criteria. Only publications in English, outlining OTC/POM misuse by adults (18 years or over) in receipt of psychological/pharmacological interventions for substance misuse were included. A third reviewer resolved disagreements if consensus could not be reached.
Data was extracted using a pilot-tested form, from full-texts of included studies to ensure a consistent approach. Heterogeneity was assessed and the Mixed Methods Appraisal Tool (MMAT) considered the risk of bias for all studies.

Results
In 2021, the database search provided 3684 results, reducing to 2047 after reviewing grey literature, hand-checking reference lists and removing duplicates. Ineligible publications were excluded, resulting in 143 potentially relevant papers. Restricting to UK-based publications reduced this to thirteen with notable heterogeneity. The third reviewer was consulted on one occasion. Meta-/subgroup analyses were not feasible due an absence of randomised controlled trials/systematic reviews, the limited consistent information available and insufficient detail across all publications; therefore, a narrative synthesis was conducted. To reduce bias risk and add robustness, all publications were included. Based on the MMAT assessment, GRADE-CERQual indicated ‘high confidence’ for all review findings, despite moderate methodological limitations.
Benzodiazepines, opioids and antihistamines were most frequently cited, and predominantly sourced online, from (various) GPs/pharmacies, street dealers and friends/family. Some older publications mentioned medicines that are no longer used in clinical practice. Adverse consequences included complications from injecting, criminal activity and withdrawal symptoms which perpetuated use. Misuse also occurred for other reasons, including desired psychoactive effect, to manage psychiatric/pain conditions and street drug shortages. There was significant variance in use, often alongside other substances, especially amphetamine, cannabis and opioids.

Conclusion
Restricting to UK-only due to the resource available notably limited the number of publications; however, this enabled a more detailed assessment and increased the relevance of findings, because there are differences in drug markets and medicine availability between countries. OTC/POM misuse is common amongst people accessing SMS and polypharmacy is concerning. A different approach to the management of OTC/POM misuse may be required: SMS improvements including withdrawal management must be considered and the need for further UK-based research was highlighted.

References
(1) Advisory Council on the Misuse of Drugs. Diversion and Illicit Supply of Medicines. London: Home Office; 2016.
(2) Gittins R, Missen L, Maidment I. Misuse of medication in adult substance misuse services: a systematic review protocol. BMJ Open 2021;11:e047283.