OBJECTIVES: The low reimbursed price of some “typical” antipsychotics could lead pharmaceutical companies to withdraw them from a given  market, as a consequence of an unfavorable cost/revenue ratio. Aim of this work was to evaluate the clinical and economic implications of such an occurrence, i.e. of the “forced  switch”  of stable psychiatric patients. METHODS: A Markov model was developed to identify all the possible scenarios related to the transition process from chlorpromazine and haloperidol to quetiapine (as possible examples). To replicate the “history” of a large number of hypothetical individual patients, a Monte Carlo simulation was performed. The outcomes of the switching and their impact were assessed using the estimated  mean frequencies of the  “lost to  follow-up”, “died” and  “stable condition” states, plus the estimated  overall number of visits and ADRs. Transition probabilities and costs, from the perspective of NHS, were taken from published literature. A sensitivity analysis was also performed. RESULTS: The “work” runs were performed with 500 cohorts of 2000 subjects each, the simulations reached convergence after 26 cycles (corresponding to one year). Data analysis allowed to infer that 91% of the patients in treatment with chlorpromazine and haloperidol would be in stable conditions after one year from switching to quetiapine and that the incidence of ADRs would be 24 for 100 patients. During the first year of treatment each patient would return to the prescribing physician between 2-3 times. The “once-only” direct cost of the transition would be 1.5 - 2.5 million euros in Italy, followed by 5-7 million per year for new drug costs. CONCLUSIONS: This simulation confirms that, for both patients and NHS, “staying” with the present therapy would represent a better and more cost effective solution than switching, even if a higher reimbursed price were to be granted.