The power of harvest moon combined with a special tonic will make the woman fertile to a demon's seed, and override any preventative measures she's taken. The demon's blood must be included in the potion.
The mixture must be taken in the morning, and impregnation must be done when the moon is high in the night's sky. The evil spawn growing inside her will influence her only for lenience so that when she does discover the truth, she will bend to the demon's will.
Appeared in The Fifth Halliwheel. Cole and the Seer laced chocolate truffles with the potion and then gave them to Phoebe so Cole could impregnant her with his demon child. Piper also ate a chocolate truffle.