Patients taking tamoxifen citrate are at risk for experiencing side effects. The serious side effects should be immediately reported to a doctor. The common side effects include hot flashes, headache, thinning hair, and nausea. The serious side effects include vision changes, signs of infection, eye pain, persistent nausea and vomiting, bruising or bleeding easily, yellow eyes or skin, mood/mental changes, dark urine, abnormal fatigue, and feet/ankle swelling.