Are the meds chlorpromazine,haloperidol, metoclopramide, phenytoin,valproic acid,&carbamazepine safe to eat to treat frequent hiccups.how long to take?

Not all of them: Usually ALL those drugs is not not safe for hiccups. All those medications used alone have been used in the past for hiccups and are relatively safe though there may be some side effects.

Frequent Hiccups can: be a serious condition. You should have an evaluation to look at your throat and stomach, chest, pancreas, kidneys and other organs.. Your doctor should also assess if this is reflux which is a condition like hiccups but treated differently. the medications that you list have all been used to suppress hiccups and all have risks of some type. With your doctor's help they can be used safely.