Ambiguity in the Effective Potential of Composite Fields

If is argued that there exists an ambiguity in the definition of the effective potential for bilocal composite fields. The ambiguity stems from arbitrariness of adding a polynomial of the source function. Physically meaningful predictions are deduced from the effective potential only when the source function vanishes. The above statement is examined in quantum electrodynamics and the Yukawa theory. A possibility of having a convenient expression of the effective potential is discussed.