…nor a sorceror… (Deuteronomy 18:10)
One may also not set himself as a wizard, using potions and brews like something out of Harry Potter. Such behavior is not only deceptive, it contains an aspect of idolatry (which is why witchcraft is a capital offense – see Mitzvah #62, “Do not permit a sorceress to live…”).
It’s actually not so simple what may or may not be witchcraft. If taking a pill for aches and pains is medicine and wearing an amulet is sorcery, what is wearing a copper bracelet? The question is whether something actually has natural curative abilities or relies on supernatural hocus-pocus for effect. People aren’t always 100% sure of why they’re doing what they’re doing. If you don’t know why crystals, aromas or the arrangement of your furniture are supposedly beneficial, it might bear looking into.
As we have said, such things are prohibited because they steal people’s minds and turn them away from God in favor of nonsense.
This mitzvah applies in all times and places. It is discussed in the Talmud in tractate Sanhedrin (pages 67a-b). It is codified in the Mishneh Torah in the eleventh chapter of Hichos Avodas Kochavim. This mitzvah is #34 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #168 of the 194 negative mitzvos that can be observed today in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.