Several housewives are speaking out in support of Andy in the wake of Leah's lawsuit earlier this week ... making it clear they've never done drugs with the 'Watch What Happens Live' host.

Kyle Richards -- who said she was one of the housewives closest to Andy -- told Page Six that she has "never seen Andy do drugs, offer drugs or do anything inappropriate ever."

Kyle went on to praise Andy as a professional -- highlighting how he even refuses to follow many Bravo stars on Instagram to keep "a distance from all of them."

"RHONJ" star Margaret Josephs was equally vocal in her support of Andy -- she said point-blank that the father of two "has never offered any 'Housewife’ cocaine.'"

Margaret -- who notably doesn't drink -- adds ... "I am appalled that someone would just go so low to assassinate and target someone’s character in that way.”

Likewise, Cynthia Bailey ...  who appeared on "The Real Housewives of Atlanta" and "The Real Housewives Ultimate Girls Trip" -- assured TMZ on Wednesday that she was "never forced" to drink and has definitely "never seen him do blow."

ICYMI ... the 'RHONY' alum hit Andy, as well as Bravo, with a discrimination lawsuit on Tuesday -- claiming the reality TV honcho created a toxic work environment, where AC allegedly used cocaine and encouraged other housewives and Bravolebrities to participate ... giving good TV edits to his favs.

A rep for Andy denied the allegations -- telling TMZ … "The claims against Andy are completely false."

'RHOC's Heather Dubrow and Meghan King have also offered up public support of Andy, applauding him for his professionalism and respect.

Leah isn't the only unhappy ex-housewife, however ... as 'RHOBH' vet Brandi Glanville also recently accused Andy of sexual harassment after he invited her to watch him hook up with another Bravo personality over FaceTime.

Andy hit back at that ... calling the exchange a joke that's been blown out of proportion.