  We present a self-consistent calculation of the finite temperature effective
potential for $\lambda \Phi^4$ theory in four dimensions using a composite
operator effective action. We find that in a spontaneously broken theory not
only the so-called daisy and superdaisy graphs contribute to the
next-to-leading order thermal mass, but also resummed non-local diagrams are of
the same order, thus altering the effective potential at small effective mass.
