Celebrities with attention deficit hyperactivity disorder

Up to 10 million American adults have attention deficit hyperactivity disorder (ADHD)—also commonly referred to as ADD—so it's no surprise that some of America's most acclaimed athletes, actors, and musicians make up part of that mix. Left untreated, the disorder is characterized by poor concentration and disorganization, and can lead to emotional and social problems.

About 60 percent of children diagnosed with ADHD will continue to experience these symptoms well into adulthood. And some people with the disorder don't receive an official diagnosis until middle age.

See which celebs have suffered with an ADHD diagnosis since childhood, and which have learned to manage their disorder as adults.

1. Michael Phelps
The 25-year-old Olympic swimming sensation is famous for his incredible focus in the pool, so it's hard to believe he has struggled with ADHD since childhood. His teachers complained about his inability to sit still until, in fifth grade, the Phelps' family physician formally diagnosed him with ADHD. At age 9, Phelps went on Ritalin; his mother, Debbie, later recalled in the New York Times that it seemed to help his hyperactivity. After two years on medication, however, Phelps said he felt stigmatized (each day at lunchtime he had to visit the school nurse to get his medicine) and asked to be taken off the drug. After consulting with his doctor, Debbie agreed to let him be med free.

Instead, Phelps used swimming to help him find focus. In fact, many children with ADHD benefit from competitive sports. "I'm just different in the water," Phelps told Sports Illustrated. "I just feel at home in it."

2. Solange Knowles
The soulful songstress says she's always been full of energy, and claims that sometimes her sporadic speech and effervescence led people to believe she was on drugs. The real culprit? ADHD.

Knowles, whose older sister is the popular singer and actress Beyoncé, said she was diagnosed with the disorder twice before she believed it. "I didn't believe the first doctor who told me," she has said. "I guess I was in denial."

Traditionally, ADHD was thought to be a male-oriented disease, and men were once believed to account for the vast majority of cases. But recent research has begun to focus on how the disorder affects females, so that ADHD may be identified earlier in women’s lives.

3. Ty Pennington
The energetic and upbeat star of ABC's Extreme Makeover: Home Edition said he was “uncontrollable” as a child unless he had a crayon and piece of paper in hand. Pennington, 44, earned poor marks throughout high school and college, until he was diagnosed with ADHD as an undergrad.

"I'm about as ADHD as you can get," Pennington told InStyle magazine. He went on medication following his diagnosis and saw an instant improvement in his schoolwork. "I immediately stared getting straight A's. It changed my life!"

More From Health.com:
Quiz: Do You Have Adult ADHD?

What Causes ADHD? 12 Myths and Facts

15 Signs You May Have Adult ADHD

4. Howie Mandel
The Deal or No Deal host is calm and collected during his super-hyped game show, but ADHD made him impulsive and unfocused well into adulthood, when he finally got a formal diagnosis.

A penchant for pranks got Mandel expelled from high school, and he continued to struggle with his attention span for the next 20 years before his doctor finally gave him an ADHD diagnosis. "I found it difficult to sit down and read a script for work, or even have a conversation," says Mandel, 55.

Mandel is a former celebrity spokesperson for a PSA campaign encouraging treatment for the disease called Adult ADHD Is Real.

5. James Carville
The political pundit and consultant is widely credited with helping Bill Clinton win the 1992 presidential election, but he wasn't always so focused. In fact, Carville, 66, initially flunked out of college.

He later went back to earn his bachelor's degree before going on to graduate from law school. Carville has said that he found his razor-sharp focus for politics because of its fast-paced and ever-changing nature. In 2007, Carville was a featured guest at the CHADD (Children and Adults With Attention Deficit/Hyperactivity Disorder) 20th Anniversary Hall of Fame Conference.

6. Christopher Knight
Playing pint-size Peter on the original Brady Bunch television series, Knight, 52, had a hard time learning his lines. Finally, in 1997, he was diagnosed with ADHD. He sought treatment to help manage his condition and served as a spokesperson for the National Consumer League's AD/HD campaign.

7. Cammi Granato
She helped lead her team to gold as the captain of the U.S. women's ice hockey team at the 1998 Olympics in Nagano, Japan—and she credits her ADHD with helping her get that far. Granato, 39, claims that constantly feeling restless contributed to her drive on ice.

ADHD makes everyday tasks such as paying bills more difficult for Granato, but the energy and creativity associated with the disorder have helped in her sport. “It’s affected me in positive and negative ways,” Granato told the St. Louis Post-Dispatch in 2005. “It’s really my worst and best qualities wrapped in one.”

This originally appeared on Health.com.