Lisa Marie Presley -- last in the news in August when she married Nicolas Cage in Hawaii and a few days later paid tribute to her dad, Elvis, in Memphis on the silver anniversary of his death -- appeared in an unusual setting Thursday, PEOPLE reports.

Presley, 34, testified before the House Committee on Government Reform in Washington, D.C., to discuss what she considers an alarming trend to medicate children for mental disorders ranging from Attention-Deficit/Hyperactivity Disorder (ADHD) to bipolar disorder.

"I have personally seen the effects of overmedicated children and it terrifies me ... especially having two kids of my own," said Presley, the international spokesperson for Citizens' Commission on Human Rights, a psychiatric watchdog group founded in 1969 by the Church of Scientology (of which she is a member). The group advocates legislation that would bar schools from forcing parents to medicate their children for ADHD and similar disorders.

Presley says her passion for this subject is purely personal. "I became involved with this whole issue because of a little 4-year-old boy, a friend of the family, who has suffered from being overmedicated," says Presley, mother of Danielle, 13, and Benjamin, 9, with first husband, Danny Keough. (They divorced in 1994 after a six-year marriage. Presley was then married to Michael Jackson from 1994-96.)

Experts believe nearly 10 million Americans under the age 18 are affected by emotional, behavioral, developmental and mental disorders. Presley's group believes millions of these children are misdiagnosed and victims of widespread and sometimes dangerous drugging in order to control their behavior -- a claim vehemently denied by psychologists and a parents' organization known as Children and Adults with Attention Deficit/Hyperactivity Disorder.

Presley told PEOPLE that her first time testifying before Congress left her "a nervous wreck, " but, she said, "I was really impressed with the whole system and with the knowledge of the Congress people. They really knew their stuff and asked good questions and got right to the point. Even the people who were on the other side of the issue seemed to understand where we were coming from."

Asked about her recent wedding to Cage, Presley replied, "Marriage ... oh, now that's a subject I'm familiar with ... You know, I've done that three times." But she declined to answer any personal questions.