Whitney Houston -- No Evidence of Doctor Shopping

Whitney Houston was not doctor shopping or using aliases to score prescriptions ... TMZ has learned.

Law enforcement sources tell us ... although the L.A. County Coroner is subpoenaing medical and pharmacy records, there is nothing to suggest Whitney or her doctors did anything inappropriate or illegal.

Sources tell us ... subpoenas will go out to 5 or 6 doctors, as well as some pharmacies that filled various prescriptions for the singer. So far, all of Whitney's doctor visits, as well as the prescriptions that were filled, seem legit.

And, we're told, the doctors and pharmacists contacted by the Coroner's Office have all been cooperative.