Introduction Management of periodontitis has in recent times shifted to the use of subantimicrobial dose doxycycline (SDD), usually at a dose of 20mg twice daily. SDD is in most cases used in conjunction with scaling and root planing (SRP) in the management of periodontitis. Studies have shown greater efficacy when the combination is used. SDD exerts its antimicrobial activity through inhibition of matrix metalloproteins (MMPs) activity. Inflammatory cells that occur in periodontal disease are implicated in the production of MMPs and these MMPs are major pathogenetic mediators in periodontal disease. The treatment usually lasts for a period of between three to nine months with the administration of 20mg of SDD twice daily. The pill burden of taking medication daily may result in decreased compliance with the SDD medication. To address this problem, modified-release drug formulations are needed to ensure once-daily dosing and as such increase compliance to medication. A modified-release system for SDD has been put in place. This system contains 40mg of doxycycline monohydrate in a capsule and is designed in such a way that it can release the active ingredient over 24 hours and as such facilitate once-daily dosing. This study aims at determining the efficacy of SDD-40 when used together with SRP in the management of periodontal disease in comparison to a placebo. In addition, the levels of subgingival flora were assessed over 9 months to determine the effect of SDD-40 on this type of flora when compared to a placebo (Preshaw et al., 2008). Methodology Study Design The study was a randomized, multicenter, double-masked, placebo-controlled study. The study was carried out over nine and a half months. It entailed a two-week screening procedure to identify participants suitable to be enrolled in the study. There was a random designation of participants to either the SDD-40 group or to the placebo group. The participants were required to take either the placebo or the SDD-40 for nine months. Participants Inclusion criteria entailed the selection of males and females who were 18 years or older at the time of screening. In addition, for the participant to be included in the study, one should have had untreated periodontal disease. On the other hand, exclusion criteria included expectant women, those with chronic conditions, and any form of dental prophylaxis in the 30 days leading to the screening process. In addition, those participants who had allergies or hypersensitivity to tetracyclines were excluded from taking part in the study. Procedures and Measures There was all-inclusive training for all individuals who were to work as examiners in the study. To reduce variability, the same examiner was required to follow the same participant throughout the study. Before the commencement of the study, the clinical attachment level (CAL) and PD of the participants were assessed and recorded, and quantified on a scale of 0-3 based on the University of North Carolina manual. The presence of periodontal disease was confirmed by the use of radiographs. To exclude any pregnant women taking part in the study, all-female participants underwent a pregnancy test. Other personal habits such as smoking, oral cleanliness, and other parameters were recorded. A total of 266 participants met the inclusion criteria and were then randomized to eithe