Abstract: Since the approval of gemtuzumab ozogamicin, an antibody–drug conjugate (ADC) targeting CD33 in 2000, 13 ADC drugs have been approved by the FDA. Although these drugs have clearly improved the survival of patients with various types of advanced cancers, their significant toxicity has compromised their therapeutic benefits. The adverse reactions of ADC drugs are complex and include on-target and off-target toxicities, where the payload drug is a determining factor. Antibody and linker may also affect the degree of toxicity. Combination therapy becomes an important strategy in anticancer treatment because of its increased efficiency, but treatment-related adverse reactions also increase accordingly. This review comprehensively analyzes the toxicity mechanisms of current ADC drugs and proposes various optimization strategies, including but not limited to optimizing linker molecules, upgrading antibody design, and changing drug administration strategies, to improve the overall safety profile of ADC drugs.