Pfizer and the National Association of Boards of Pharmacy on Thursday announced the start of an educational campaign to explain the dangers of counterfeit drugs and help people find legitimate pharmacies online.

The effort includes a website called AWARERx.com, a video series on a new YouTube channel called youtube.com/spotfakemeds, and takeovers of websites counterfeiters have previously used to sell knock-offs of Pfizer medicines.

Counterfeit drugs can be very dangerous, containing toxic substances such as rat poison or lead, or they can have the wrong amount of the real drug’s active ingredient.

In addition, people who buy medicines from illegal online pharmacies risk financial fraud and identity theft if they provide credit card or other personal information.

New York-based Pfizer, the world’s biggest drug maker by revenue, said counterfeit versions of its medicines have been sold in at least 101 countries.

Sham versions of at least 40 Pfizer products have been detected in those countries, including Alzheimer’s treatment Aricept, painkiller Celebrex, cholesterol fighter Lipitor, blood-pressure drug Norvasc, antidepressant Zoloft and Viagra.

Estimated worldwide sales of counterfeit medicines topped $75 billion last year, up 90 percent since 2005, according to the World Health Organization. Meanwhile, one in six Americans bought medicines on the Internet last year.

“Counterfeit medicines are often produced in unsanitary conditions by people without any medical or scientific background,” Patrick Ford, Pfizer’s head of global security in the Americas, said in a statement.

Among other advice, the US Food and Drug Administration urges consumers to check Internet pharmacy sites for a seal indicating they are licensed pharmacies and sell approved medicines.

The blue, oval-shaped seal reads “National Association Boards of Pharmacy,” around the red letters VIPPS, short for Verified Internet Pharmacy Practice Sites. A list of sites with that accreditation is at VIPPSpharmacies.net.

The pharmacy association is a national professional group for individual state pharmacy boards, which regulate pharmacists and pharmacies, both brick-and-mortar ones and online operations.

The national group recently reviewed more than 8,000 websites selling prescription drugs, determining that 96 percent appeared to not be following pharmacy laws or standards for practice.