If the cabinets are properly built and properly hung, they will hold considerable weight. You have to rely on the cabinet maker for the first. There is a strip of wood on the backside of the cabinet at top and bottom. That is where the screws go to secure it, and they must be into the studs. Tney(cabinet screws) should be 2 1/2" min length and should be #12 or bigger. Drywall screws not recommended, usually #9. Two screws per stud, one top one bottom of the cabinet.