Periodontal disease can be treated in several ways. This paper reviewed whether antimicrobial photodynamic therapy (aPDT) in addition to scaling and root planing (SRP) produces improved clinical results over systemic antibiotics (ABs) in conjunction with SRP in adults with periodontitis. Studies were searched using the following electronic databases: MEDLINE, the Cochrane Database of Systematic Reviews, and the Web of Science Core Collection up to and including November 2018. Four randomized controlled trials (RCTs) were reviewed to maximise the reliability of the evidence. All participants suffered from either chronic or aggressive periodontitis and each study contained SRP as an adjunct to ABs or aPDT. To determine whether groups showed improvement after treatment, the outcome parameters chosen were probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP). Despite finding significant improvements in all groups, the differences among groups were not consistently statistically significant. The lack of homogeneity in the results among these studies indicates that it was not possible to determine a conclusion about whether aPDT or AB as an adjunct to SRP provides better improvements in periodontitis as measured by PD, CAL, and BOP. Further studies with more similar study designs are required before firm conclusions can be deduced.