The new study finds bad reactions, including hallucinations, paranoia and confusion, sent more than 19,000 people to ERs in 2010. That's a 220 percent increase from 2005.
Two-thirds of the cases involve women. Doctors say that's because it stays in their systems longer and, they add, women should take a lower dose.
The drug's manufacturer says it stands behind the substantial body of clinical data demonstrating the safety and efficacy of Ambien.
More than half of those who went to the ER had mixed the sleeping pill with another drug or alcohol, which can boost side effects.