Yes, people have used SN without stronger prescription meds and still succeeded. The main concern is vomiting. SN is harsh on the stomach. Without antiemetics like metoclopramide or domperidone, there's a real chance you'll throw it up before enough is absorbed, which can lead to failure, intense nausea, or ending up in hospital.
Otc options like antacids (e.g. nexium or famotidine) can help protect the stomach lining, but they don't prevent vomiting. Some people try motion sickness tablets like meclizine or dimenhydrinate, but these are hit or miss and far less effective than proper antiemetics.
If you have to go without meds, absolute fasting (no food or drink for 6โ8 hours beforehand), a calm setting, and mental preparedness become even more important.