To allow Tamiflu to work on the flu you need to take the Tamiflu 48 hours before the onset of the flu which helps to kill off the flu virus before it takes full effect on your body.
Sometimes Tamiflu can make you feel worse for a bit before it actually gets rid of the flu but those bad feelings should not last long.
Tamiflu can usually cause some side effects such as vomiting, nausea, and even hallucination but they don't last long and taking Tamiflu is great to help get rid of the flu before it gets too bad.
But you must take the Tamiflu within 48 hours before the onset of the flu otherwise it will not work.