Why do some dentists refuse to prescribe phenergan along with hydrocodone?

[melturco]

My past dentists prescribed me phenergan with my hydrocodone to aid with nausia, otherwise the pain killer makes me sick. My new dentist told me that he does NOT prescribe phenergan and that other dentists should not either. He did not explain why, and I would like to know why. (He instead went on to prescribe me Vicodin, which as you know ALSO has hydrocodone in it, but with no phenargan prescription.)

1) What is the general feeling in the dentist world when it comes to prescribing phenegran with pain killers?
2) What is taught about this or written about it journals?
3) Why would a dentist refuse to prescribe it yet others prescribe it?

Thanks.