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Background Adjuvant endocrine therapy is key treatment in early oestrogen receptor positive breast cancer (BC). In premenopausal BC ovarian function suppression (OFS) in combination with tamoxifen or aromatase inhibitor (AI) is commonly used, particularly in high-risk patients who have received chemotherapy. The profound suppression of circulating oestradiol associated with OFS could have adverse cardiovascular and metabolic effects, We aim to evaluate the reported adverse effects within randomised phase III trials in premenopausal women with BC. Methods A systematic search of online databases was conducted to identify randomised control trials (RCTs) involving OFS which reported adverse events (hypertension, weight gain, thrombosis, cardiac ischemia, glucose intolerance and hyperglyacemia). Pooled odds ratios (OR) with 95% confidence interval (CI) were estimated using a random-effects model. Results Four RCTs were included in the metanalysis with a total of 7808 patients, separated into 3 main treatment groups: Tamoxifen, OFS plus Tamoxifen and OFS plus AI. We found that OFS increased risk of hypertension when compared to Tamoxifen alone (7.6% vs. .4.8%, OR 1.49,95%CI 1.09–2.01; P = 0.01). Tamoxifen with OFS increased risk of thrombosis when compared to AI with OFS (1.7% vs. .0.7%, OR 2.87,95%CI 1.19–6.9; P = 0.02). Conclusions This highlights the possible impact of OFS in premenopausal women as it increases risk of developing hypertension which may require closer monitoring and initiation of early treatment. There appears to be a protective effect of AI when compared to Tamoxifen in terms of thrombosis. Further studies are needed to explore the impact of these drugs on the cardiovascular health of these young women with BC.