Transcript for Online Prescription Drug Dangers
watchdog tonight, an alert about the online pharmacies. 1 in 6 americans buying medication online, without a prescription. Tonight, the fda is warning that the vast majority, 97% of those online pharmacies, are not legal. Some, even receiving counterfeit drugs that may be dangerous, even deadly. Here's abc's jim avila now. Reporter: It's a moving target of as many as 40,000 active online pharmacies, a huge majority of them fly by night start-ups, that the fda warned today sell at a cut-rate price but deliver expired, contaminated an fake drugs that could harm the consumer. You have no assurance of the safety, efficacy or quality of those products. Reporter: How easy is it to set up an online pharmacy? Two uc-san diego medical researchers showed me how they set up their own fake drug store using search engines, facebook and twitter to draw potential buyers. So, do you have to have a pharmaceutical degree to set up one of these websites? Oh, not at all. We basically created a web ad which has a medical professional, a picture of a person that we just purchased, and we were able to post it online without any verification or requirements at all. Reporter: It's so easy, setting up a hit-and-run pharmacy is lightning fast to start, and even faster to disappear before authorities can catch up. The bad guys know when they're getting chased, so they just shut down in a minute and then literally within another hour, they've set themselves right back up again. Reporter: There are some legitimate online pharmacies -- about 2%, says the alliance for safe online pharmacies. How can you tell? Watch out for sites that allow you to buy drugs without a prescription. Offer deep discounts that seem too good to be true. Send unsolicited e-mails offering cheap drugs. And are located outside the u.S., Beyond the reach of regulators. The important messages are, have a prescription, know your online pharmacy, make sure it is safe and take your medication as directed. Reporter: The danger is fakes cannot only sicken or kill outright, they can cause a resistance to real medicine or carry hidden side effects. Dangerous stuff.
This transcript has been automatically generated and may not be 100% accurate.