Purpose <p>Aqueous suppressants (AS) are commonly used after glaucoma drainage device (GDD) surgery to limit early rises in intraocular pressure (IOP). This review aims to evaluate whether the timing or regimen of postoperative aqueous suppression influences IOP control, the hypertensive phase (HP) incidence, surgical success, postoperative complications and visual outcomes.</p> Methods <p>A systematic review of PubMed, Scopus, and Web of Science was conducted. Studies evaluating postoperative AS initiation after GDD surgery were included. Studies involving combined procedures, except clear-cornea phacoemulsification, were excluded.</p> Results <p>Seven studies were included: three randomized clinical trials (RCT), three retrospective cohort studies, and one case series. All studies involved exclusively Ahmed glaucoma valve (AGV) implantation. Regarding timing, early AS initiation was evaluated in five studies and was associated with a significantly lower HP incidence in two of them. Despite heterogeneous definitions of surgical success and failure, three studies showed either higher success rates or lower failure rates compared with delayed initiation. Only one RCT demonstrated consistently lower IOP values across all follow-up visits up to 1 year. In a paediatric RCT, prolonged aqueous suppression resulted in lower IOP and reduced hyperencapsulation at 1 year. Regarding IOP-lowering drug class, one study found that AS achieved better IOP control, reduced long-term need for glaucoma medications, and higher success rates compared with prostaglandin analogues. Earlier initiation did not increase the rates of hypotony or major complications.</p> Conclusion <p>Early AS initiation after AGV implantation is associated with lower HP incidence in several studies, but the certainty of evidence is low to moderate and long-term benefit remains uncertain.</p>