Who made Juliet's sleeping potion?

In Romeo and Juliet, Friar Lawrence gives Juliet a potion that will put her in a comatose state. She will appear to be dead, but will really just be in a deep sleep. This will allow her to escape her family so she can be with Romeo. The plan is that her family will lay her in a tomb, and Friar Lawrence will arrange for Romeo to meet her there when she wakes up.
Friar Lawrence proposes this plan to Juliet when she comes to visit him, claiming she will kill herself before marrying Paris. Friar Lawrence says:

Take thou this vial, being then in bed, And this distilled liquor drink thou off; When presently through all thy veins shall run A cold and drowsy humour, for no pulse Shall keep his native progress, but surcease: No warmth, no breath, shall testify thou livest; The roses in thy lips and cheeks shall fade To paly ashes, thy eyes' windows fall, Like death, when he shuts up the day of life; Each part, deprived of supple government, Shall, stiff and stark and cold, appear like death: And in this borrow'd likeness of shrunk death Thou shalt continue two and forty hours, And then awake as from a pleasant sleep.

Unfortunately, Romeo does not receive the letter from Friar Lawrence. He believes Juliet is truly dead, and so he receives poison from the apothecary (a person who prepares and sells drugs, or medicine).