Popular TV doctor  Mehmet Oz had to swallow a bitter pill Tuesday, when a Senate investigative committee grilled him over diet-pill ads that make claims without scientific evidence.

“My show is about hope,” Oz said while testifying in a hearing on deceptive advertising, according to CBS News. “We’ve engaged millions in programs – including programs we did with the CDC – to get folks to realize there are different ways they can rethink their future.”

Committee Chairwoman Sen. Claire McCaskill, D-Mo., told Oz his “miracle” weight-loss drug had lots of detractors.

“The scientific community is almost monolithic against you in terms of the efficacy of the three products you called ‘miracles,’” she said. “I don’t get why you need to say this stuff when you know it’s not true. When you have this amazing megaphone, why would you cheapen your show?”

Oz admitted “that my enthusiastic language has made the problem worse at times,” but pointed out that companies take his words and use his photograph without permission, according to The Hollywood Reporter.

“I know you feel that you’re a victim, but sometimes, conduct invites being a victim,” McCaskill said. “I think that if you would be more careful, maybe you wouldn’t be victimized quite as frequently.”

The public is particularly vulnerable to diet aid claims, she said, adding, “People want to believe that you can take an itty-bitty pill to push fat out of your body.”

U.S. Sen. Amy Klobuchar, D-Minn., told Oz his popularity gave him added responsibility.

“You can use your knowledge and celebrity status to do good things, and right now, it seems we’re going the opposite way here,” she said.

Oz said he wanted to be a part of the solution and was now curbing his language.

“I am in the situation where I’m second-guessing every word I say on the show now,” he told senators.

Dr. Oz’s endorsement can prove influential. In May 2012, CBS News reported, a green coffee bean extract pill he touted on his show sold a half a million bottles. The Federal Trade Commission later sued a Florida company selling the pills, claiming false advertising.