Why does a pharmacist need to verify a prescription?

Because the pharmacist is the person that is legally responsible for making sure the patient gets the correct medication. Getting the wrong medication can have tragic consequences. Example: An incorrect dose of Coumadin (warfarin) could lead to severe internal bleeding.

Also, the pharmacists checks to make sure the medication is compatible with other medications on profile and proceeds to tell the patient if there are any side effects or importants things to know while taking the medication. Example: Phenazopyridine turns your urine a dark orange/copper color.

Sometimes, the prescribing physician may have overlooked some of these facts about medications or may simply just not know. They have a lot on their plate already. Or sometimes a patient may see many doctors so the prescribing physician may not be aware of all the medical conditions present.