Drusus the Younger died in AD 23 while occupying the position of Tiberius's principal surviving son and an important figure in the imperial succession. At the time, his death was treated as the result of illness. Years later, after the fall of Sejanus, accusations emerged that Sejanus and Drusus's wife Livilla had arranged his poisoning, with members of the household allegedly assisting. The surviving Roman histories give that explanation considerable prominence, but the allegations were developed amid political reprisals and testimony obtained under coercion. They do not provide the certainty of a modern toxicological investigation. A cautious account therefore distinguishes the reported illness and death from the later claim of deliberate poisoning. The precise substance, treatment and sequence of symptoms cannot be reconstructed securely. His death changed the balance among the imperial heirs, drawing greater attention to the sons of Germanicus and eventually affecting the position of Drusus's own children. Those dynastic consequences help explain why later writers scrutinized the event so closely. They do not prove every private act attributed to Livilla or Sejanus. Drusus's ending remains a death surrounded by substantial suspicion, with natural illness and a court conspiracy not separable on the surviving evidence with medical certainty.