Background: Periodontal diseases are prevalent oral health conditions characterized by inflammation and destruction of the supporting structures of the teeth. Conventional treatments include mechanical debridement and antimicrobial therapy. Subantimicrobial dose doxycycline (SDD) has emerged as a promising adjunctive therapy due to its anti-inflammatory properties while avoiding antibiotic resistance concerns. Materials and Methods: A randomized clinical study was conducted involving 100 patients diagnosed with chronic periodontitis. Participants were divided into two groups: Group A received scaling and root planing (SRP) along with placebo, while Group B received SRP along with SDD (20 mg twice daily). Periodontal parameters including probing pocket depth (PPD), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded at baseline, 3 months, and 6 months post-treatment. Results: At 6 months, Group B demonstrated a statistically significant reduction in mean PPD (from 5.8 mm to 3.2 mm, p < 0.001) and CAL (from 7.1 mm to 4.3 mm, p < 0.001) compared to Group A. Additionally, BOP scores decreased by 50% in Group B compared to 30% in Group A. Adverse events were minimal, with no significant difference between the groups. Conclusion: The adjunctive use of SDD in the management of periodontal diseases significantly improved clinical outcomes, including reductions in PPD, CAL, and BOP, compared to conventional therapy alone. SDD represents a valuable addition to the armamentarium of periodontal treatment modalities, offering effective anti-inflammatory benefits with minimal adverse effects.