Statins are cholesterol-lowering drugs used by millions of Americans to battle cardiac disease. However, there is concern that the drugs shouldn't be prescribed without limits.

Patricia Thomas has coronary artery disease and takes statins to keep her cholesterol in check.

“It keeps the arteries from getting blocked,” she said.

Statins are prescribed to reduce the risk of fatty deposits which can cause life-threatening clots in the blood stream.

A recent study suggested that millions more people – even those without high cholesterol – could benefit from statins. However, new research found the drugs could harm people whose cholesterol levels are already low.

The risks are "associated with some mental problems, (such as) processing, depression, maybe some mental illness, concentration,” said Dr. David Langer, with St. Luke's Roosevelt Hospital.

Cholesterol helps release chemicals called neurotransmitters in the brain. They help carry messages between brain cells. Researchers discovered when brain cells are deprived of cholesterol, they are five times less effective.

The researchers say doctors should be wary of prescribing statins to healthy people, but patients like Thomas do benefit from the drugs.

"It's just one less thing for me to worry about and I feel safe,” Thomas said.