In Juliet’s chambers, Juliet thanks the nurse for helping her to pick out clothes and jewels for the wedding, but asks the nurse to leave her be for the evening so that she might privately atone and prepare. Lady Capulet enters and asks if Juliet needs any help getting ready, but Juliet says everything is set and again reiterates that she wants to be left alone for the rest of the night. The nurse and Lady Capulet bid Juliet goodnight and leave. After they’ve gone, Juliet calls out a halfhearted farewell to them—she is not sure when she’ll ever see them again.
Earlier in the play, Juliet used wordplay in conversation with her mother to say one thing while meaning another. But now her use of language with her mother and the nurse is different. She simply lies to them. This shift makes clear that Juliet’s loyalty has completely shifted—she no longer feels any duty to her family, instead viewing Romeo as the one to whom she owes her true loyalty.
As Juliet pulls out the vial and prepares to drink from it, she admits that she’s afraid—she’s worried about many possible kinks in the plan she and Friar Laurence have made. If the potion doesn’t work, she’ll have to marry Paris; on the other hand, if it works but lifts too soon, she’ll wake up in the crypt where all her kinsmen are buried, and might go mad upon seeing the remains of Tybalt and countless generations of other dead Capulets. Worse still, Friar Laurence may, she fears, have given her poison in order to put an end to Juliet and cover up his involvement in the whole affair. Even though Juliet is terrified, she decides to go through with her plan. She lifts the vial and makes a toast to Romeo before drinking and falling, almost immediately, upon her bed.
Juliet is taking the potion as a way of expressing her love for and commitment to Romeo—but finds herself perturbed and distracted by violent thoughts as she considers doing what needs to be done in order to be reunited with her love. Ultimately, Juliet decides that any of the terrifying unknowns she’s facing are better than losing the chance at a life with Romeo and swallows the potion as a way of escaping her familial duties and obligations.