Greetings. Your method of usage on minoxidil is fine.No changes needed unless you are having any discomfort or unless your treating dermatologist advises any changes. As far as onion juice is concerned - its role in hair growth in androgenetic alopecia is contorversial - that apart - I am concerned - what if the juice causes any irritation or burns - then you'll lose the hair that you already have, think about it! Warm regards, Dr Govind Suresh Mittal, Bengaluru.