Historians do not know for certain that Alexander the Great was murdered. However, there are two main accounts of his death and both stories indicate that he could have been assassinated with poison.
One account is by Plutarch. In this story, Alexander the Great was visited by an admiral. He drank with the admiral and a close friend throughout the evening and into the next day. Shortly after, he developed a fever before becoming extremely ill. He died after his illness.
Another story tells that Alexander the Great drank a large amount of wine and began to feel sick. He then became weak and suffered from pain before dying. In both stories, he became ill after drinking. It is possible that someone could have poisoned his drink.
Assassination was common in Alexander the Great's time. Modern theories suggest that he died from typhoid fever, or possibly liver disease due to heavy drinking.