Any reader of Tacitus' Annals may have noticed that poison played a prominent part at the imperial court during the Early Principate. In this article seven cases of suspected poisoning, mentioned by Tacitus in his Annals, are analysed and commented upon in some detail. The use of poison in general is studied against the background of Roman society, culture and mentality. It is argued that modern ideas about physicians, pharmacists, poisons and drugs may induce anachronistic interpretations of the texts. If the ambiguous position of the doctor, the root cutter, the drug-seller, the magician and of their products is taken into account, some cases of poisoning prove to be much more equivocal than they seem at first sight. It is likely that they are the unintentional result of medical practice – or of black magic.