That's the idea for the buds to get big and heavy. The plant will not grow as tall and will instead grow outwards. I have that problem of the buds getting to big and fat. Yes it can and will break the steam off. That's why you use string and tie them to the roof. Or you use a tomato cage and support them that way. Or you use stakes to support them.

Anyway you look at it it's a good thing the buds get big and heavy.

If you grow them right the main stock is about 3-4" girth or larger anyway.