More concerns are being raised about the safety of the most commonly prescribed antidepressants in children.

Studies in animals suggest that Prozac (search) and other SSRI antidepressant (search) use in children could lead to weaker bones in adulthood.

The findings come just two weeks after another animal study linked early use of selective serotonin reuptake inhibitor (SSRI) antidepressants like Prozac to an increased risk for depression and anxiety disorders later in life. And less than a month ago, federal officials ordered manufacturers to include warnings on SSRI antidepressant labels about a possible increase in suicidal thoughts and behaviors among children and adolescents who take them.

Child psychiatrist David Fassler, MD, worries that the recent news surrounding Prozac and other SSRI antidepressants could lead to the undertreatment of children and teens with depression. Fassler testified on the subject at an FDA hearing in September.

“SSRI antidepressants can be extremely helpful for some, but not all, children and adolescents who suffer from depression, but medication alone is rarely a sufficient intervention for complex child psychiatric disorders,” he tells WebMD.

Bones Narrower, Weaker

In the newly published study, bone development from birth to adulthood was measured in a group of mice bred to mimic SSRI antidepressant exposure. Compared with normal mice, the genetically altered animals had smaller, less dense bones during development. The same was true for another group of normal mice exposed to Prozac early in life. The findings are reported in an online edition of the journal Endocrinology.

“Bones in the exposed mice were not shorter, but they were narrower and bone mass was reduced,” lead researcher Stuart J. Warden, PT, PhD, tells WebMD. “This is especially significant because we now know that bone health early in life is important for ensuring bone health during adulthood.”

Warden, who is an assistant professor at Indiana University School of Medicine, says lab studies linking serotonin pathways to bone growth led him to do the animal studies. SSRI antidepressants interfere with these pathways, so the assumption was that the SSRI antidepressants could inhibit bone growth.

The findings raise important questions about the effect of SSRI antidepressants on bone development that need to be addressed in human studies, he adds.

Other antidepressants, such as Cymbalta and Effexor, also affect serotonin and could potentially have the same effect.

Elderly Women on SSRI Antidepressants

One such study was presented last month at the Seattle meeting of the American Society of Bone and Mineral Research. Researchers reported an increase in hipbone loss among postmenopausal women taking SSRI antidepressants. The antidepressant users lost bone at about twice the rate as nonusers.

Warden says the weight of the clinical evidence still favors the use of SSRI antidepressants in many severely depressed children and teens. Fassler agrees.

“Depression is a very serious condition in children and adolescents,” the University of Vermont School of Medicine psychiatry professor says. “Studies suggest that over 40 percent will attempt suicide at least once, and depression also increases the risk of substance abuse and ongoing problems at home and at school. The good news is that we really can help most kids who suffer from depression. The real tragedy is that there are still so many kids who aren’t getting the comprehensive treatment they need.”

By Salynn Boyles, reviewed by Michael W. Smith, MD

SOURCES: Warden, S. Endocrinology, online edition. Stuart J. Warden, PT, PhD, assistant professor, department of physical therapy, Indiana University School of Medicine, Indianapolis. David Fassler, MD, associate professor, department of psychiatry, University of Vermont College of Medicine, Burlington. American Society of Bone and Mineral Research 26th Annual Meeting, Seattle, Oct. 1-5, 2004. WebMD Medical News: "Early Exposure to Prozac May Up Anxiety Risk."