HPTP is a monoaminergic neurotoxin related to MPTP. It is the dehydration product of haloperidol. The agent is specifically a dopaminergic and serotonergic neurotoxin. HPTP is a prodrug of HPP<sup>+</sup>, which mediates its monoaminergic neurotoxicity. This is analogous to how MPP<sup>+</sup> mediates the neurotoxicity of MPTP. Other related compounds include RHPTP and RHPP<sup>+</sup>.