Why do i wake up most mornings with a thick white coated tongue?

Food debris: A white coating on your tongue is mainly food and bacterais debris. It is worse in someone with a dry mouth or allergies. You can use a tongue scraper or a toothbrush to remove it and this should be part of your daily oral hygiene routine. This can be a cause of bad breath.

Bacterial growth: That is a result of reduced salivary production and flow while you sleep, resulting in bacterial growth during sleep. Saliva helps wash away bacteria and it also has an antibacterial component to it, so when there is less saliva, you have more bacteria. This is why it's important to brush and floss your teeth before going to bed to reduce bacteria before sleeping.

Poor oral hygiene: The thick white coating could either be plaque (bacteria) or a fungal infection. If it's bacteria, you might want to get a dental check-up to make sure there is not a rotten tooth or periodontitis happening in your mouth.