How do you know if someone is addicted to lortab?

Yes, this is too many. Your friend might take more pills than that in the entire day - some of which you are not aware of. To help his back pain please advise him to lose some of the weight as being overweight can contribute heavily to chronic back pain problems.

How many was he prescribed a day? He may need more medication to relieve his pain as pain is very subjective and we can not tell what another is feeling.
Of course he is taking too much. The base product of asprin or tylenol alone in his mediction is way too much and can be very harmful. Anytime one takes more medication than is prescribed, it is too much, no matter what that medication is.
He needs to talk to his doctor and tell him that his prescribed dose is not helping. There may be another medication that would give him relief without taking more than has been prescribed for him.