How is the phrase “an effective amount” interpreted in patent claims?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The interpretation of the phrase “an effective amount” in patent claims can vary depending on the context and disclosure. The MPEP provides the following guidance:

• The phrase may or may not be indefinite, depending on whether one skilled in the art could determine specific values based on the disclosure.
• It may be considered definite if the amount is not critical and skilled artisans can determine it from the written disclosure, including examples.
• It may be indefinite if the claim fails to state the function to be achieved and more than one effect can be implied from the specification or relevant art.

As stated in MPEP 2173.05(c): “The proper test is whether or not one skilled in the art could determine specific values for the amount based on the disclosure.”

Recent cases have tended to accept “an effective amount” as being definite when read in light of the supporting disclosure and in the absence of prior art that would create uncertainty about the claim’s scope. For example, in Ex parte Skuballa, 12 USPQ2d 1570 (Bd. Pat. App. & Inter. 1989), a pharmaceutical composition claim reciting “an effective amount of a compound of claim 1” without stating the function was held to be definite when read in light of the supporting disclosure.