It's up to your pharmacy and your insurance and your prescriber. Most pharmacies and insurance companies prefer to mail out prescriptions and consequently charge less for them. They also like to send them in three month supplies. I don't think there are any regulations against it; though it may not be possible for scheduled drugs like sleeping pills. My former psychiatrist had no problem with that and Walgreens charged me less and Coventry insurance covered more of the cost. For some reason my new psychiatrist won't prescribe in 3-month increments but I don't know why.