No pharmacological therapy is approved to treat methamphetamine physical dependence, but it has been hypothesized that serotonin (5-HT)-enhancing drugs might limit the severity of withdrawal symptoms. To test this hypothesis, we used a planarian model of physical dependence that quantifies withdrawal as a reduction in planarian movement. Planarians exposed to methamphetamine (10 µM) for 60 min, and then placed (tested) into drug-free water for 5 min, displayed less movement (i.e., withdrawal) than either methamphetamine-naïve planarians tested in water or methamphetamine-exposed planarians tested in methamphetamine. A concentration-related inhibition of withdrawal was observed when methamphetamine-exposed planarians were placed into a solution containing either methamphetamine and 5-HT (0.1 – 100 µM) or methamphetamine and the 5-HT1A receptor agonist 8-Hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) (10, 20 µM). Planarians with prior methamphetamine exposure displayed enhanced withdrawal when tested in a solution of the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-(2-pyridyl)cyclohexanecarboxamide (WAY 100635) (1 µM). Methamphetamine-induced withdrawal was not affected by the 5-HT2B/2C receptor agonist meta-chlorophenylpiperazine (m-CPZ) (0.1 – 20 µM). These results provide pharmacological evidence that serotonin-enhancing drugs inhibit expression of methamphetamine physical dependence in an invertebrate model of withdrawal, possibly through a 5-HT1A-like receptor-dependent mechanism.