Jan. 7--Nausea, drowsiness and weight gain.

Millions of Americans taking antidepressants have already traded side effects like these for a lift in mood and a reduction in anxiety. But researchers at Texas Tech's Health Sciences Center say people taking the most common group of antidepressant drugs -- selective serotonin reuptake inhibitors -- might face another problem.

"We're trying to find out if people taking these medications are at risk for osteoporosis," said Michalea Daggett, a pharmacotherapy specialty resident at the HSC. Previous studies in older adults have shown a link between the use of SSRIs -- like Prozac -- and decreased bone mineral density, which can lead to osteoporosis, Daggett said.

The researcher and her colleague, Charles Seifert, are now studying whether SSRIs have similar bone-weakening effects in younger adults. "We're looking for people age 30 to 40 who have been on one of these drugs for at least two years," Daggett said. More than 10 percent of Americans take antidepressants, making them the most commonly prescribed class of drug in the U.S., a 2009 Archives of General Psychiatry article reported.

SSRIs are the frontline in treating the disease, and may also be prescribed for anxiety disorders and attention deficit hyperactivity disorder, according to the Mayo Clinic Web site.

Although the cause isn't fully understood, inadequate levels of the neurotransmitter serotonin in the brain might cause depression in some people, according to Mayo. The SSRI drugs counter depression by blocking the re-absorption of serotonin by nerve cells in the brain, which leads to enhanced neurotransmission and improved mood.

But the brain isn't the only place where serotonin has a job to do, said Seifert, who is a professor of pharmacy practice at the school.

And the SSRI's action to block serotonin uptake by bone cells might result in the breakdown of bones, Seifert said.

"Animal data clearly shows serotonin receptors in bone are key to the accumulation and maintenance of bone," he said.

Seifert said the researchers have already investigated the relationship between SSRIs and bone loss in a college-aged sample. While they didn't see osteoporosis in the 52-person sample, they did show "a very strong correlation between how long they were on SSRIs and (a drop in bone density)."

"That's what led to this study; we wanted to look at people who were a little older but not postmenopausal," he said.

Daggett said the team uses ultrasound waves to measure bone density in the heel. The free consultation takes about 10 minutes, and participants will be advised if they are at risk for osteoporosis.

"We'll give participants a note they can take to their physicians," Daggett said.

The goal of the study is not to see patients taken off their SSRIs, Seifert said.

Instead, the researchers believe people taking them should be screened for bone loss.

"If they know they are at risk, they have options," Seifert said. "They can take calcium or vitamin D or bisphosphonates."

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