Analysis of clinical trials on drugs targeting dopamine receptors: a scoping review

Dopamine receptors are G protein-coupled transmembrane proteins that mediate dopamine-dependent neurotransmission in the central nervous system via intracellular signaling cascades. Through their involvement in motor and cognitive processes, they are involved in various neurological diseases and their symptoms, including Parkinson's disease and schizophrenia. The pharmacological modification or antagonization of dopamine receptors is therefore highly relevant. Dopamine receptors have been studied across diverse conditions, yet the resulting clinical evidence is scattered and highly heterogeneous, with no structured synthesis to date. This fragmentation limits the ability to evaluate the broader clinical relevance of dopamine receptor modulation, and a synthesis of these heterogenous trials represents a research gap. By systematically mapping and summarizing available trials, this review provides an integrated overview and highlights areas where further research is needed. The aim of this scoping review was to analyze current and completed clinical studies on dopamine receptors. Because the field of dopamine receptor-targeted therapies is broad, complex, and not yet systematically mapped, a scoping review offers the methodological flexibility to capture this diversity and synthesize current knowledge. ClinicalTrials.gov was searched for trials on dopamine receptors. Studies with a focus on any dopamine receptor were included, while studies employing dopamine receptors and related medications as comparators were excluded. Search results were evaluated based on the condition, the type of intervention, the study location, the sponsor, and the outcome. Two hundred forty-five. trials on dopamine receptors were identified. One hundred ninety-two (78.4%) trials were interventional trials and 53 (21.6%) were observational studies. Ten trials were terminated before completion. More than one-third of the studies (38.3%) were conducted in the USA. Most trials (n = 151) were sponsored by sponsors other than industrial or governmental entities, primarily by clinics and medical centers of universities. The most frequent indication was schizophrenia (n = 20, 8.0%), followed by Parkinson's disease (n = 18, 7.2%), tobacco abuse (n = 8, 3.2%), alcoholism (n = 7, 2.8%), and other substance abuse (n = 7, 2.8%). Thirty-eight trials (15.5%) were classified as "Has results," while for 207 trials (84.5%), no results were available. Of the trials with results, 17 had publications in which the results were reported, with 20 studies published in total. While numerous trials have been conducted on dopamine receptors, the outcome from these studies in terms of scientific publications is low. The reasons for this low output must be investigated in future studies.