Some shady Internet sites are sending customers in the U.S. counterfeit and potentially dangerous drugs.

The Food and Drug Administration says people who ordered Ambien, Xanax, Lexapro and Ativan from these rogue sites wound up with Haloperidol, a powerful anti-psychotic drug.

"In fact, some people sought emergency medical treatment for symptoms that they got after taking the drugs," says the FDA's Ilisa Bernstein. The people who got sick had difficulty breathing, muscle spasms and muscle stiffness.

Bernstein says the Internet makes it's hard to track down the crooks selling these potentially dangerous drugs.

"A consumer will order from one web site, they receive a confirmation of their order from another Web site, their credit card will be billed by yet a third Web site and in the end they receive this yellow envelope from Greece that contained a drug they didn't order."

One thing to look for when shopping at an online pharmacy is the VIPPS seal. It shows that this cyber-drugstore meets the standards of the National Association of Board of Pharmacy.

For More Information:

FDA Alerts Consumers to Unsafe, Misrepresented Drugsurchased Over the Internet

See photos of bogus drugs

Buying Drugs Online Is No Trivial Matter

Buying Drugs Online: It's Convenient and Private, but Beware of 'Rogue Sites'

Buying drugs from Canadian online pharmacies can equal big savings, but first know your sources.

Tips for Buying Drugs Safely Online