Neurochemical probes are starting to tease apart several neurotransmitter systems that are involved in suppressing feeding. Instead of a classical medial hypothalamic lesion, neurotoxins or neurochemical inhibitors can be used to produced animal models of the obese. These models make it clear that amphetamine and fenfluramine do not act in the same way. In addition to actions on brain synapses, these drugs may act directly or indirectly on the receptors that monitor energy availability. Phenylpropanolamine (PPA) apparently has anorectic action within the lateral hypothalamus, but this could be due to a number of actions such as: (a) an adrenergic synaptic effect, (b) a direct receptor effect, (c) an indirect effect on glucoreceptors caused by increasing glucose utilization, or (d) some combination of these. In addition, these drugs taken systemically could activate similar mechanisms peripherally, thereby prompting a barrage of cues to and from the brain. Throughout this discussion it has been emphasized that the therapist who uses any of these drugs, needs to be aware of the possible changes in mood, behavior and physiological signs that are thought to occur in animals. Eventually the therapist will be able to take advantage of these side-effects to coordinate the drug's style with that of the patient.