Background: CDK4 and CDK6 are cyclin-dependent kinases that control transition between G1 and S phases of the cell cycle, hence controlling cell cycle progression by reversible combination with cyclin D1. In cancer cell, CDK4/6 activity is overexpressed, which can lead to amplification or overexpression of the genes encoding for CDK 4/6 or the cyclin D. Additionally, loss of endogenous INK4 inhibitors can also lead to over activity of CDK4 and CDK6. We undertook a meta-analysis of randomized controlled trials (RCT) to determine the risk of gastrointestinal (GI) and hepatic toxicities associated with CDK 4/6 inhibitors. Methods: We conducted a comprehensive literature search using MEDLINE, EMBASE databases, and meeting abstracts from inception through September 2018. In our analysis, we incorporated RCTs that mention GI toxicities and elevation of aspartate aminotransferase (AST) or alanine aminotransferase (ALT) as adverse effects. Mantel-Haenszel (MH) method was used to calculate the estimated pooled risk ratio (RR) with 95% CI. Random effects model was applied. Results: A total of 4,557 patients with advanced breast cancer from 7 phase III and 1 phase II RCTs were eligible. The study arms used were palbociclib/ribociclib/abemaciclib or placebo in combination with letrozole or anastrozole or fulvestrant or other hormonal agents. The RR of all-grade side effects were as follows: diarrhea, 1.691 (95% CI: 1.220–2.345; P=.002); nausea, 1.632 (95% CI: 1.447–1.840; P<.001); vomiting, 1.684 (95% CI: 1.256–2.259, P=.001); stomatitis, 2.160 (95% CI: 1.332–3.503; P=.002); elevated AST, 1.832 (95% CI: 1.312–2.558; P<.001); and elevated ALT, 2.150 (95% CI: 1.649–2.803; P<.001). The RR of high-grade side effects were as follows: diarrhea, 2.592 (95% CI: 0.853–7.877; P=.093); nausea, 1.326 (95% CI: 0.589–2.988; P=.496); vomiting, 1.089 (95% CI: 0.479–2.476; P=.839); stomatitis, 2.097 (95% CI: 0.502–0.753; P=.310); elevated AST, 2.274 (95% CI: 1.173–4.410; P=.015); and elevated ALT, 3.988 (95% CI: 2.387–6.663; P<.001). Conclusions: Our study demonstrated that the risk of developing all grade GI toxicities and all grades of hepatic side effects including grade 3 and 4, was high in CDK 4/6 inhibitors group, compared to control arm, and prompt intervention with good supportive care is required.