  In this paper we introduce a new procedure, termed by us \emph{energy
formalism}, to deal with dissipative systems in metric theories of gravity.
This approach aims at determining the analytic expression of Rayleigh
dissipation function in the context of the inverse problem in the calculus of
variations. We describe our method in detail, presenting a simple example.
After, we consider as first extensive application the general relativistic
Poynting-Robertson effect. The obtained results and future implications are
discussed.
