Is it absolutely prohibited to eat or drink using the left hand?

Always eat and drink with your right hand. We know the Prophet sallallahu alayhi wa sallam said in a hadith in Sahih Muslim: 'The believer eats and drinks with his right hand and shaitan eats and drinks with his left hand.' So it's highly highly important and a highly encouraged sunnah to always eat with your right hand. If it's somebody who's maybe been used to eating or drinking with the left hand or maybe children or maybe somebody's left hand and that's become the norm for them, then try as much as you can to train yourself over time to use your right hand. And inshallah Allah will make it easy for you.