ABC News' Lisa Stark and Enjoli Francis report:

Pop an Ambien - or its generic version, zolpidem - and you're supposed to get a good night's rest. But according to a new study released today, a growing number of users are ending up in the emergency room because of adverse reactions to the medication.

The study by the U.S. Substance Abuse and Mental Health Services Administration found that adverse reactions to the sleeping pills - which may include hallucinations, paranoia, confusion and drowsiness - sent nearly 19,500 people to ERs in 2010, a 220 percent increase from 2005.

According to IMS Health, combined prescriptions for zolpidem and Ambien increased from 39 million in 2008 to almost 44 million in 2012.

Credit: JB Reed/Bloomberg/Getty Images

Dr. Bob Rothstein, an emergency physician and vice president of medical affairs at Suburban Hospital in Bethesda, Md., said zolpidem is a safe drug.

However, he added, "If it's used more and more by a lot of people, you're going to see those side effects. … It's just a law of averages."

Forty percent of those who ended up ERs in 2010 had taken the sleeping pill alone. The remaining 60 percent had mixed it with other medications, such as pain relievers and antidepressants, as well as alcohol. All of the combinations can boost the side effects.

In the new study, women users seemed especially vulnerable. They made up two-thirds of the ER visits in 2010. Of those nearly 44 million prescriptions for Ambien and zolpidem in 2012, about 64 percent or more than 29 million were filled for women.

"I think we know that women clear the drug from their system more slowly than men and, in fact, the FDA recently recommended a lower dose for women just recently," Rothstein said.

In January, the Food and Drug Administration said that the manufacturers of Ambien, Ambien CR, Zolpimist, Edluar and other sleeping medications that contain the active ingredient zolpidem must lower their recommended doses for women.

The decision came after a series of clinical trials and driving simulation studies showed that even after eight hours of sleep, zolpidem levels in women may be high enough to impair alertness in tasks, including driving.

Sanofi, the company that manufactures Ambien, said in a statement today that patients should consult with their health care professionals regarding their specific treatment regimens.

"Sanofi takes all matters of patient safety seriously and we stand behind the substantial body of clinical data demonstrating the safety and efficacy of Ambien and Ambien CR, which were approved by the FDA in December 1992 and September 2005, respectively, amounting to 20 years of real-world use and 23 billion nights of patient therapy worldwide," the statement said.

Rothstein said zolpidem should not be used for a long period of time.

"You become less sensitive to the drug over time so you will need more and more and you might mix it with other drugs so you're just putting yourself at risk," he said.