Pharmacological and human studies with a highly potent opioid peptide, D-Met2, Pro5-enkephalinamide.

D-Met2, Pro5-enkephalinamide (DMPEA) is an opioid peptide having analgesic activity in animals more potent after intravenous administration than morphine. It is less toxic but in animals it showed a higher dependence capacity than morphine. Besides analgesia DMPEA produces in rodent behavioral symptoms similar to those evoked by morphine or beta-endorphin, resembling the actions of neuroleptica. In human trials DMPEA was found to produce unpleasant sensations, no euphoria, and sometimes even dysphoria. DMPEA increases the serum levels of prolactin, growth hormone and, to a less extent, of TSH. Those effect of DMPEA on pituitary hormones. Finally, the human studies indicated that DMPEA antagonized pain (measured with the submaximum effort tourniquet technique), but did not affect adversely and even improved attention and short-term memory; it had no effect on the long-term memory. As the subjective effects of DMPEA are not pleasant, and no patient desired to obtain another treatment, some optimism as to low habit-forming properties of DMPEA may be justified.