  A Hamiltonian effective potential (the logarithm of the square of the wave
functional) is defined and calculated at the tree and one loop levels in a
$\phi^4$ scalar field theory. The loop expansion for eigenfunctionals is
equivalent to the combination of WKB expansion and an expansion around constant
field configurations. The results are compared with those obtained from the
Lagrangian effective potential. While at tree level the results from the two
methods coincide, at one loop level they differ. Our result at one loop level
is that the reflection symmetry is not broken at $m^2\geq0$.
