N-didesmethyl Loperamide, an active metabolite of the peripheral μ1-opioid receptor agonist loperamide, impedes electrically induced contractions in isolated guinea pig myenteric plexus (IC50 = 370 nM) and enhances the sensitivity of a chloroquine-resistant P. falciparum strain to chloroquine (EC50 = 482 nM). Notably, it achieves this without causing toxicity in A-10 vascular smooth muscle cells (IC50 = >10,000 nM).