The Truth Spell

The Truth Spell was created by Brad Kern and Constance M. Burge for the hit TV series Charmed.

It is a spell in the Warren Book of Shadows that allows the caster to obtain the truth from anyone they speak to.

The spell lasts for twenty-four hours after which all memories of that period are erased. Only the caster will remember all that is said. Once this is a personal gain spell, there is a backfire: the caster has to speak the truth to anyone as well.

History
For more information about the spell in Charmed please visit Charmed Wiki

Charmed
In 1998, Prudence Halliwell cast this spell to find out what her than boyfriend, Andy Trudeau would truly think when she told him that she was a witch. When she told him, Andy couldn't accept it. However, when the spell wore off, he forgot about the incident. Prue broke up with him, thinking that it would be better to end the relationship now instead of later.

Later, when Andy discovered that Prue was a witch, she told him about the spell and it turned out that Andy was fine with Prue being a witch. However, he told her that no matter whether he had a minute, a month, or a year to think about it, his decision would have been the same. He wanted to have a normal life to come home to, complete with a white picket fence, a two car garage, a screaming kid, a wife to kiss - but no demons or warlocks. Andy said that it could be because of all the evil he dealt with everyday on the job that he didn't want it at home to. Prue understood, knowing that she wanted exactly the same thing, but she couldn't have it.

A few years later, in 2003, Paige Matthews cast this spell for the same reason as Prue did. She was dating a guy named Nate Parks. Paige thought, since he had a Celtic tattoo, that he might accept her as a witch. Paige saw a future with Nate and thus cast the spell. Nate was very accepting of Paige's magic, but he also revealed that he was married and had two children. Paige immediately broke off their relationship and, in order to protect their secret, asked Darryl to put him in the local jail until his memory was erased. Darryl, with great reluctance, did so and kept him there until the spell wore off.

Later that day, Paige cast the spell again on her grandmother, Penny, so that she would reveal her true feelings for The Necromancer. Grams revealed that she still loved the Necromancer, but that her love for her family was much, much stronger. She then vanquished the Necromancer. The next day, a confused Nate was confronted by Paige, who broke up with him again, as he had forgotten the events of the previous day.

Aunty Dearest
In Aunty Dearest, Chris used this spell to see how Andrea would react to knowing that Chris and his family are witches. Andrea reacted well when Chris told her about him as his family, but the backfire was that when Chris told Andrea the truth about - without the truth spell, she didn't take it well.

The Truth Spell
For those who want the truth revealed, Opened hearts and secrets unsealed, From now until it's now again, After which the memory ends. Those who now are in this house, Will hear the truth from other's mouths.

Notes & Trivia

 * Prudence and Paige used the spell for the same purpose: to find out if their boyfriends could accept them being witches.
 * There is also a potion which works the same way as the spell does. It was used by Paige in Charmed though there is no information on it.
 * Prue was the one who gave Chris the idea of using the spell. She thought to use it herself when she was dating Eric.