My friend has had a headache on his right side of head for a week it still hasnt gone is it serious?

Go check it out!!!: You can't assume here. He must get it checked out by his doctor or er. A lot of headaches, even simple tension type pain can present on one side only. But he needs a physical exam and possible ct/mri to make sure nothing more serious is going on. Once you know that, then he can be treated for the usual causes of neck/head pain.

See a physician: Headaches can eminate from simple non threatening causes, to very serious possibly life threatening conditions. It is not possible to diagnose the cause of the headache without a physical exam, and probably a brain MRI or scan. I would suggest seeing a neurologist immediately, and possibly visiting a hospital er (not a doc in the box er) where appropriate scanning can be accomplished.

May be: New onset headaches may be a symptom of serious condition. Your friend must see a doctor.