Background: Urinary drug screens are routinely administered for patients returning from leave from forensic psychiatric wards, and are required to be negative for patients to continue to use their allocated leave. Case: A 35-year-old woman took leave from her low-secure psychiatric unit. On return, her urine screened positively for 3,4-Methylenedioxymethamphetamine (MDMA). She strongly denied she had taken it; however, all her leave was cancelled. Her clinical state greatly deteriorated, and she attempted to hang herself the following day. After stabilisation of the patient and continued denial of taking MDMA, the urine was sent for toxicology analysis. In the weeks that followed, she started self-harming and deteriorated to the point of needing electroconvulsive therapy. The toxicological report came back as a false-positive due to recently started Mebeverine. Conclusion: Clinicians must be mindful that urinary drug screens are not diagnostic, but also that not being believed can be devastating, especially for long-stay forensic inpatients.. Please contact the library to request a copy of this article - http://bit.ly/1Xyazai