11/08/2011 at 10:00 AM EST
The rumors can be put to rest.
Apparently Real Housewives of Beverly Hills
star Kim Richards's slurred speech and strange behavior are a result of the combination of medications she's taking, not illegal drugs or alcohol, according to her costar, Dr. Paul Nassif.
On Monday's episode, during a consultation with Adrienne Maloof's plastic surgeon husband, Richards, 46, revealed she's been taking the anti-anxiety medication Lexapro, the antidepressant Trazadone, and Topamax, an anti-seizure medication which can be used to treat alcoholism.
"I'm glad you told me this, because now it all makes sense," Nassif tells her. "[The combination] is going to make you slur the words a little bit. It's going to make you out of it."
"You have that sedated look on you right now," he added.
Richards's bizarre behavior has drawn concern from her costars, including Nassif himself. On a recent episode, new cast member Brandi Glanville
described Richards as being "wasted out of her f––ing mind"
and accused her of using crystal meth.
And in last year's season finale
, Kim's sister Kyle Richards accused her of being an alcoholic.
"I am afraid that people think I'm drinking," Kim admitted on Monday's episode. But she insisted she wasn't mixing the medications with alcohol and hadn't had anything to drink "for a while."
"This is why everyone's going, you know, 'Is she on something right now?'" Nassif reiterated. "It's the damn medication."
Kim also had an emotional exchange with her sister
later in the episode, after confessing that she planned move in with her new boyfriend.
"For once in my life, I just want to do something that I want to do," Kim said.
"I just want you to be happy," a tearful Kyle responded, "but I don't think you are."