The phrase "cast doubt on" is a common expression used when questioning the validity or reliability of information. However, there are plenty of other synonyms that can be used interchangeably to convey the same idea. One such term is "raise questions," as it denotes an uncertainty or lack of clarity surrounding a specific topic. Another possible synonym is "undermine," as it suggests the reduction of trust or belief in something. Likewise, "challenge," "discredit," and "question" are all applicable alternatives that can be used to convey skepticism or doubt in a particular situation, idea, or belief.