Evidence-based decision making examines the validity of the information, the design of clinical trials and the application of statistics so that the clinician can select a therapeutic option that best suits the pet, client and problem. Many drugs used in veterinary behaviour fall into the poorest level of evidence including personal experience, colleague opinion, continuing education, textbooks, in vitro studies or studies from other species. The soundest evidence (A) requires systematic reviews of randomised controlled clinical trials (RCT) or at least a single RCT with high confidence. Most drugs licensed for veterinary behavioural use have been through one or more RCTs as well as pharmacokinetic and safety studies, and have the added benefit of the manufacturer's technical support. While the practitioner must follow the prescription cascade, the best evidence may be a drug that is licensed for another application, another species or in another country (for which a human version is available). When dose, compliance or availability is an issue compounding might be considered; however, stability and storage are a concern. In addition, for transdermal medications, bioavailability of fluoxetine was 10%, while systemic absorption of amitriptyline and buspirone was minimal (compared to oral dosing). Psychotropic drugs should be used with informed consent as to any off-label use and potential adverse effects.