Iv dramamine or iv phenergan (promethazine) for.motion sickness? which is better if the person is already actively vomiting

Hospital: If you are at the hospital then let the hospital decide that. Do not try this yourself as you can risk other complications. Usually though IV Phenergan (promethazine) is used most of the time for nausea where as dramamine is usually taken 30 minutes before known motion sickness.

Motion sickness: Iv medications would not be used initially for motion sickness, and dramamine (dimenhydrinate) only comes in oral form (not iv). Oral dramamine (dimenhydrinate) and scopolamine patches can prevent motion sickness. Iv meds are best given in a clinic, doctor's office, or er where the doctor and staff can select medicines based on individual assessment. Treatment differs if it's a migraine variant vs other cause.