The phrase "is impaired" refers to a state of being weakened, damaged, or otherwise limited in ability. Some synonyms for this phrase might include "is handicapped," "is compromised," "is hindered," or "is disabled." Other related terms might include "is debilitated," "is incapacitated," "is diminished," or "is restricted." When describing a person's ability to perform a task or function, you might also use terms like "is challenged," "is limited," or "is unable." Whatever term you choose, it should accurately convey the idea that someone or something is not functioning at full capacity.