Background and Objectives: Periodontal infections tend to be site-specific, mostly confined to the periodontal pocket. Therefore, much attention has been garnered towards local drug delivery and adjunctive agents as to prevent potential side effects and increased antibiotics resistance with systemic antimicrobials use. However, the question of the most efficient local drug delivery or adjunctive agent for dental practitioners to utilise and provide the maximum benefits to their patients remains unanswered. This review aimed to provide insight on the efficacy of current commercially available local drug delivery and adjunctive agents used in non-surgical periodontal therapy in adults treated for periodontitis. Data/Sources: The PubMed/MEDLINE (via Ovid), EMBASE (via Ovid) and CENTRAL databases were searched to identify any randomised controlled human intervention studies with professionally applied local subgingival drug delivery and adjunctive agents used in the treatment of periodontitis. The search considered works published till April 2019 using specific keywords pertaining to the topic. Bibliographies from previous systematic reviews on the topic were scrutinised. Only articles published in the English language were selected, and the use of experimental or discontinued drugs was excluded. Study selection: The longest follow-up studies of each local delivery system were selected, and 24 randomised controlled trials that compared non-surgical mechanical therapy with and without an adjunctive agent were identified. The details of each system and their clinical results were summarised in table form. Conclusions: Overall, various commercially available local subgingival drug delivery and adjunctive agents have been clinically tested in the non-surgical treatment of periodontitis. However, the methodologies and clinical results vary within and between each system. Therefore, it is difficult to conclude and support the superiority of one local adjunctive agent over another. Further well-designed medium to long term studies are needed as their usefulness is still debatable, considering the cost-benefit ratio with modest clinical results. Keywords: periodontitis, local delivery, adjunct, non-surgical periodontal therapy, subgingival application