When Friar Lawrence gives Juliet the vial and says, "When presently through all thy veins shall run / A cold and drowsy humour; for no pulse / Shall keep his native progress, but surcease," he means that the contents of the vial will cause her to appear dead. This potion is designed to induce a deep sleep that will mimic death, allowing her to escape her current situation and avoid marrying Paris. So, the correct answer is:
The contents of the vial will cause her to appear dead.