  A model for quantum Zeno effect based upon an effective Schr\"odinger
equation originated by the path-integral approach is developed and applied to a
two-level system simultaneously stimulated by a resonant perturbation. It is
shown that inhibition of stimulated transitions between the two levels appears
as a consequence of the influence of the meter whenever measurements of energy,
either continuous or pulsed, are performed at quantum level of sensitivity. The
generality of this approach allows to qualitatively understand the inhibition
of spontaneous transitions as the decay of unstable particles, originally
presented as a paradox of quantum measurement theory.
