Counterfeit drugs are a major problem in the developing world, where retail chains like Walgreens don’t exist and pharmacists sell drugs out of small, family-run shops. Counterfeiters insert fakes—which often contain chalk or lead-based paint—at different points in the supply chain. They often sell directly to pharmacists, who think they’re buying a discounted version of the real thing. According to the United Nations Office on Drugs and Crime, counterfeit drugs represent a $1.6 billion annual market in Africa and Asia alone.

A handful of entrepreneurs are trying to make drug sales more reliable. Pharmasecure focuses on India. Aegate operates in Europe. And Sproxil– a mobile phone-based startup in Boston– works in Nigeria.

Ashifi Gogo co-founded Sproxil two years ago, when he was an engineering graduate student at Dartmouth. Gogo decided to focus on Nigeria, he says, because the Nigerian government is proactive about fighting counterfeit drugs, and Nigeria—the most populous country in Africa– has a strong cell phone culture and “a lot of swindlers.”

Sproxil places scratch-off labels on bottles and blisters– the small aluminum pouches that contain pills. When users scratch off the labels, they see a numerical code. They send that code, via text message, to a toll-free phone number, and immediately receive a text back that indicates whether or not the drug is legit.