In the play's final scene, poison kills (or aids in the killing of) Hamlet, Queen Gertrude (Hamlet's mother), Laertes (Polonius's son and Ophelia's brother), and King Claudius (Hamlet's uncle and step-father).  Further, Claudius used poison to murder Old King Hamlet before the start of the play.  Thus, poison is responsible for the deaths of the entire royal family as well as Laertes, who was once held up as a possible replacement king by the people.  

When Marcellus said, "Something is rotten in the state of Denmark," he was right (1.4.100).  It is as though corruption, since the old king's death by poison has spread -- like poison -- throughout the entire royal family.  When Claudius poisoned the king, he set into motion the metaphorical spread of this "rot" until it consumes them all.  Claudius was corrupted by the cruel murder he performed, Gertrude was corrupted by Claudius's deception and her own lust, Laertes was corrupted by his need for revenge (he does not behave honorably in his duel with Hamlet), and Hamlet was corrupted by his own inability to act and cowardice.  Now, the entire royal family and the family closest to them have been completely ruined.  However, with the spread of the poison, through all of their deaths, the rot has been eradicated and Denmark can now begin anew with fresh leadership.  

What is Shakespeare saying about the theme "poison" in Shakespeare's play Hamlet?

[eNotes editors are only permitted to answer one question per posting. Additional questions should be posted separately.]

These are excellent themes from Hamlet. I wish I could answer all of them. One that intrigues me is "poison."

This is something we literally see several times in Shakespeare's Hamlet. First of all, we learn from the Ghost that Old Hamlet was poisoned while he slept in the garden/orchard when his brother poured poison in his ear. We "see" this again when the players reenact the murder of Old Hamlet in the "play-within-a-play." Finally, we witness the use of poison in the last scene, where Laertes holds a poisoned blade that cuts Hamlet and Laertes. Claudius poisons the wine with the pearl, which Gertrude drinks. Then when Laertes implicates the King, Hamlet stabs the King with the poisoned sword and forces him to drink the poisoned wine. These are just the literal uses of poison in the story.

In terms of figurative uses of poison in the story, we can see many examples of this as well. When Laertes leaves for school, and again when Polonius arrives on the scene, both men try to poison Ophelia's thoughts regarding Hamlet, telling her that he does not love her and never will.

We might assume that Claudius, in a charming manner, poisons Gertrude's mind after losing her husband—to marry Claudius. The Ghost admits that one might be tempted (speaking of Gertrude) by "lewdness court[ing...] in a shape of heaven, So lust, though to a radiant angel [be] linked, will sate itself in a celestial bed (I.v.59-61).

The Ghost also tells Hamlet: "But howsoever you pursue this act, / Tint not thy mind nor let thy soul contrive / Against thy mother aught." In other words, the ghost of Old Hamlet tells Hamlet not to "poison his mind" or take action against Gertrude. (Twice he will tell Hamlet to leave her to heaven.)

Hamlet himself poisons the relationship between himself and Ophelia, telling her to join a nunnery, never to marry, and that he does not love her—all because he does not trust her. This will do some serious damage.

Ophelia's mind is poisoned between the warnings of her father and brother against Hamlet, Hamlet's rejection of her, and her father's death—and she goes insane.

When Hamlet confronts Gertrude about her relationship between her and Claudius, Hamlet reveals the poison within Claudius, and even in her relationship with her husband's brother. She clearly sees how she has sinned against the memory of her husband, and how her new husband has killed Old Hamlet, and it eats at her like a poison within.

Lastly, we see Claudius as he poisons the mind of Laertes by laying the guilt for Polonius' death and the madness of Ophelia at Hamlet's door. He manipulates Laertes until his heart is poisoned, as is Claudius' soul. However, it is not only because of things that Hamlet has done and Claudius' fear of Hamlet's knowledge of his murderous actions, but also because the people outside the castle have been calling for Laertes to be their king—another obstacle in Claudius' path.

The theme or concept of poison can be seen throughout the play, not just literally as a substance that stops life, but also figuratively as something that harms the hearts, souls and minds of the characters in the play. And most of the poison can be traced back to Claudius who begins the tragic chain of events when he poisons his brother— Old Hamlet—as he is sleeping.