My 59yr dad has this white lesion on the side of tongue.at first it was red then he took medication prescription by dr.for herpes but still there.what can it be?

Tongue lesions?: What type of 'dr' prescribed the medication? How long has it been since he stopped the medication? You can either follow through by having your dad return to the doctor who prescribed the medication for a follow up visit, or.......Have him seen by a general dentist or oral surgeon (or ENT specialist) for a diagnosis and treatment as\if necessary.

Oral surgeon: How long has it been there? Is it painful? How big is it? Is it getting bigger? Does he smoke? Does he drink? These are just a few questions that may be asked when your father sees an oral surgeon. If the lesion looks suspicious the surgeon may perform a biopsy. Best of luck to your father.

See dentist: Lesions on the side of the tongue can be a variety of things. Have your father see his dentist. They may recommend a biopsy to evaluate further.