The few disadvantages of OOP are:

1. Size:

Object-Oriented programs are much larger than other programs. In the early days of computing, space on hard drives, floppy drives and in memory was at a premium. Today we do not have these restrictions.

2. Effort:
Object-Oriented programs require a lot of work to create. Specifically, a great deal of planning goes into an object-oriented program well before a single piece of code is ever written. Initially, this early effort was felt by many to be a waste of time. In addition, because the programs were larger (see above) coders spent more time actually writing the program.

3. Speed:
Object-Oriented programs are slower than other programs, partially because of their size. Other aspects of Object-Oriented Programs also demand more system resources, thus slowing the program down.

4. Not suitable for all types of problems:
There are problems that lend themselves well to functional-programming style, logic -programming style, or procedure-based programming style, and applying object-oriented programming in those situations will not result in efficient programs.

5. Not all programs can be modeled accurately by the objects model. If you just want to read in some data, do something simple to.it and write it back out, you have no need to define classes and objects. However, in some OOP languages, you may have to perform this extra step.

6. The objects often require extensive documentation.