Frequency of drug misuse has increased in the society and also in psychiatric patients. It´s known that drugs have a negative influence in psychiatric pathology, so its identification is very important for a better prognosis.

We aim to demonstrate that drug misuse draws out the stay in hospital of psychiatric patients and increases the number of readmissions needed, basing the hypothesis on our laboratory information of drug screening in a psychiatric hospital.

It is analyzed, retrospectively, all admission to a short stay unit in a psychiatric hospital in 2000 and 2005, and compared all patient with a positive result in a urine sample obtained by a drug screening protocol with the rest of admissions to that unit, measuring in both groups the number of readmissions, and the extension of hospitalization.

Our hypothesis is confirmed, being the number of readmissions more frequent and the extension of hospitalization longer when patients are drug-users.

Prevalence of drug misuse has met increased in the last decade and more frequently among mental patients. Drug misuse difficults psychiatric treatments and increases sanitary expenses, being important stablishing diagnostic and treatment measures to face this problem So it`s important to take under consideration that this behaviour affects negatively in the progress of hospitalization, as proved in our investigation.