The drug Risperdal is commonly prescribed to kids with autism and attention deficit disorder (ADD) to help with behavior problems. But there is a little known side effect for some boys: development of breasts.

The anti-psychotic has been prescribed to hundreds of thousands of children since it came on the market 14 years ago, despite limited approval from the U.S. Food and Drug Administration for use in kids. Now the families of boys who developed breasts after taking the medication are suing drug maker Janssen, claiming the company marketed Risperdal for unapproved uses and buried information about the possibility of breast growth.

Risperdal can cause the body to increase production of a hormone that makes breasts grow. One boy was just 4-years-old when he developed a breast on one side. And even after undergoing mastectomies, some boys still say they feel like girls.

It’s unclear how common breast growth is in people who take Risperdal, but in a study conducted by Janssen 43 out of 1,885 children experienced the problem.

As for the company, they contend that the possibility of breast growth is clearly indicated on the warning label that comes with the prescription, reports CBS News.

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