Potions please

The story of Tristan and Isolde must be the first to mention a love potion. It is also, as far as I can see, one of the few to explore the consequences, or lack of them, of drinking such a potion.
The story is that Tristan is bringing the fair Isolde back from Ireland as a wife for his uncle, King Mark. Image via Wikipedia
On the way, the pair manage to drink a love potion that means they fall in love. In some versions they are tricked into drinking it, in others they do it with full knowledge. They continue their journey, Isolde marries Mark, but the two lovers are constantly sneaking away to spend time with each other. The potion, of course, frees them from any responsibility for their actions.
Queen Isolde prepared the potion as a way to ensure that her daughter and King Mark fall in love. Is it something that all Queens get taught? Knowledge of these kinds of things seems taken for granted in fairy tales.
Beyond this, fairy tales that feature magic potions are pretty rare. As far as I can tell. There are a few such as The Little Mermaid, Snow White (kind of), The Water of Life, The Black Bull of Norroway, Donkey Cabbages, the Blue Bird and a few others.
Reading a few fairy tales made me realise that the world they depict is pretty damn strange. Plus some of the basic laws of this world reveal themselves. For instance, if you go weeping in a garden or forest someone will turn up to help you. Usually they have magical powers and will offer to help you in return for you aiding them. These bargains often do not turn out well.
Of course, the whole moral landscape of the fairy tale has been ably mapped out and classified by Antti Aarne and Stith Thompson. Vladimir Propp did the same but with more emphasis on the function of the motifs in the stories. There is even a webpage that lets you generate your own Proppian folk tale. I just tried it and got this as a sample par...
"From the corner of my eye, I saw the man from the mountain open his razored jaw and draw a poisoned needle from underneath his tongue. I watched the needle fly from his finger through my father's ear and out the other, turning all his fluids into ones of pure jade and stone. Then the foreigner strapped my jaded father to his back and continued to ride into forbidding wastelands."