Is probiotic (beneficial bacteria) sourced from an animal or human, and prescribed by a doctor to improve gut health, permissible (halal) or forbidden (haram)?

It is not permissible to take medicines made from an unslaughtered animal or from a human body unless it has transformed into another substance. However, if it is taken from a permissible, ritually slaughtered animal, there is no objection to its use. If the impure substance does not transform into another substance, it remains in its original state, which is impurity, and its use is prohibited.