What is the similarities of diet cola and cola?

They both contain Cola.

Anybody can use Cola however, you are not allowed to use any registered brand name i.e. Coke Cola and Pepsi, that would breach copy right laws etc.

Both products are made from syrup each recipe is tweaked to give it their own stamp.

Theoretically you could go out tomorrow and make your own Cola brand,

but why would you?

the funding set up is ridiculous and people are becoming more self aware of drinking sugary or carbonated drinks.