The parent comment does not claim it's not approved by the FDA. They simply say it's toxic at the wrong dose, which your source says as well. It is something

The parent comment does not claim it's not approved by the FDA. They simply say it's toxic at the wrong dose, which your source says as well. It is something that can easily be taken wrong (given it has interactions with other meds), that's why people should take it under the direction of a doctor.