Branwyn's Tears

Branwyn's Tears; also known as Aeval's Joy, and Fergus's Sweat, is a heavy, clear oil that smelled of cinnamon and vanilla, it was first introduced in A Kiss of Shadows. It is a powerful fey aphrodisiac; the oil is said to make a human or lesser fey into a sidhe lover for a night or turn even a sidhe into a sexual slave.

No glamour can stand against the touch of Branwyn's Tears because no amount of concentration can stand against it's power. It's power is all encompassing when in contact with bare skin.

A Kiss of Shadows
While Meredith was undercover, investigating the Alistair Norton case for The Grey Detective Agency, Alistair used some of the oil on her skin. She was unaware of the spell until after it had taken effect. Merry realized her mistake too late, and she lost control over her glamour. She tried to turn the energy of the aphrodisiac to violence unsuccessfully. The sidhe who gave Alistair the Tears persuaded him to pour the entire bottle over Merry, trying to drive her mad.

After her rescue from attempted rape and possible death, she was questioned by a Detective Alvera who did not believe her when she told him of the Tears, insisting that no love or lust potion ever worked. She asked permission to touch him with her oil drenched hand to convince the officer that the danger was real. Unfortunately, once the oil touched him, he grabbed Meredith and kissed her, breaking her control over the oil, and the two had to be forcibly parted, Alvera buried under a pile of male officers, Meredith under females, some of whom also became infected with the touch of the oil - a young uniform, Riley, also had to be forcibly pulled from Meredith. Jeremy had to be brought in to ward Meredith to protect both her and the officers.

Once at home, Meredith's lover, Roane covered himself in the oil in order to be a sidhe lover for Merry for a single night. Through this act - a ritual of sorts - Meredith was brought into her power.

Consequences
There were two possible punishments for giving Branwyn's Tears to a mortal. The first was death. The second was to be covered in Tears and left alone without any means of relief for six months.

As punishment for giving the Tears to a mortal, Andais sentenced Cel  to be covered in Branwyn's Tears and left alone for three months. When Cel's people attacked Meredith, and tried to kill her, Meredith insisted that the Queen order Cel to serve the full sentence of six months.