How long before treatment should you administer an antiemetic to alleviate nausea?

Well first off. An antiemetic alleviates vomiting. And that depends on the reason for the vomiting. If it is viral, it's better to let it run it's course to get it out of your body. If it's nausea. Eat a cracker. If your administering an antiemetic prior to treatment or surgery, it's to prevent vomiting, as in during a surgical procedure. Patients are advised not to take in any meds without physicians say so. Nurses, we follow physicians orders! but it is usually just before.