While you are not legally "forced" to pack all medication in your hand luggage, it is strongly recommended by travel experts and airlines to keep all essential and life-saving medications in your carry-on. Checked bags can be lost, delayed, or subjected to extreme temperature fluctuations in the cargo hold that can degrade the quality of certain drugs like insulin or biologicals. By keeping your medication with you, you ensure it is available if you experience a flight delay or a long layover. In 2026, TSA and international security rules allow you to carry liquid medications in containers larger than 3.4oz (100ml) as long as they are "medically necessary," though you should declare them at the security checkpoint. Always keep medications in their original pharmacy packaging with your name clearly visible on the prescription label to avoid issues at customs. For pills, a 3–5 day "emergency supply" should be the absolute minimum kept in your hand luggage, even if the rest of your supply is in your checked suitcase.