Background and Purpose: In patients with acute ischemic stroke with large vessel occlusion, the role of intra-arterial adjunctive medications (IAMs), such as urokinase, tPA (tissue-type plasminogen activator), or glycoprotein IIb/IIIa inhibitors, during mechanical thrombectomy (MT) has not been clearly established. We aim to evaluate the efficacy and safety of concomitant or rescue IAM for acute ischemic stroke with large vessel occlusion patients undergoing MT. Methods: We searched Medline, Embase, and Cochrane Stroke Group Trials Register databases from inception until March 13, 2020. We analyzed all studies with patients diagnosed with acute ischemic stroke with large vessel occlusion in the anterior or posterior circulation that provided data for the two treatment arms, (1) MT+IAM and (2) MT only, and also reported on at least one of the following efficacy outcomes, recanalization and 90-day modified Rankin Scale, or safety outcomes, symptomatic intracranial hemorrhage and 90-day mortality. Data were collated in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results: Sixteen nonrandomized observational studies with a total of 4581 patients were analyzed. MT only was performed in 3233 (70.6%) patients, while 1348 (29.4%) patients were treated with both MT and IAM. As compared with patients treated with MT alone, patients treated with combination therapy (MT+IAM) had a higher likelihood of achieving good functional outcome (risk ratio, 1.13 [95% CI, 1.03–1.24]) and a lower risk of 90-day mortality (risk ratio, 0.82 [95% CI, 0.72–0.94]). There was no significant difference in successful recanalization (risk ratio, 1.02 [95% CI, 0.99–1.06]) and symptomatic intracranial hemorrhage between the two groups (risk ratio, 1.13 [95% CI, 0.87–1.46]). Conclusions: In acute ischemic stroke with large vessel occlusion, the use of IAM together with MT may achieve better functional outcomes and lower mortality rates. Randomized controlled trials are warranted to establish the safety and efficacy of IAM as adjunctive treatment to MT.