效果不佳英语短语怎么说

"Not effective" or "ineffective" are common ways to describe something that is not performing well or producing the desired results. Here are a few more phrases that may be used to describe something that is not working well:
Not producing the desired results
Not achieving the intended outcomes
Not successful
Not yielding the desired results
For example: "The new marketing campaign has been ineffective at generating leads. We need to come up with a different strategy."