Melanocyte-inhibiting factor (MIF-1) is a peptide fragment derived from oxytocin that produces multiple effects, including blocking opioid receptor activation, acting as a positive allosteric modulator of dopamine receptor subtypes, inhibiting release of neuropeptides, and potentiating melatonin activity. MIF-1 has been investigated for its antidepressant, nootropic, and anti-Parkinsonian effects and is resistant to metabolism in the bloodstream. Other related peptides include Tyr-MIF-1 and endomorphin-1 and -2.