Researchers examined data from more 350 previous studies that tested more 400,000 drug samples in low- and middle-income countries. Overall, roughly 14 percent of medicines were counterfeit, expired or otherwise low quality and unlikely to be as safe or effective as patients might expect.
"Low-quality medicines can have no or little active pharmaceutical ingredient [and] can prolong illness, lead to treatment failure and contribute to drug resistance," said lead study author Sachiko Ozawa of the University of North Carolina at Chapel Hill.
"Or it may have too much active ingredient and cause a drug overdose," Ozawa said by email. "If it is contaminated or has other active ingredients, then the medication could cause poisoning, adverse drug interactions or avertable deaths."
Much of the research to date on counterfeit or otherwise unsafe medicines has focused on Africa, and about half of the studies in the current analysis were done there.
Almost one in five medications tested in Africa were fake or otherwise potentially unsafe, researchers report in JAMA Network Open.
Another third of the studies were done in Asia, where about 14 percent of medicines tested were found to be counterfeit or otherwise unsafe.
Antibiotics and antimalarials were the most tested drugs in the analysis. Overall, about 19 percent of antimalarials and 12 percent of antibiotics were falsified or otherwise unsafe.
While fake or improperly made medicines undoubtedly harm patients, the current analysis couldn't tell how many people suffered serious side effects or died as a result of falsified drugs.
Researchers did try to assess the economic impact of counterfeit or improperly made medicines and found the annual cost might run anywhere from $10 billion to $200 billion.
While the study didn't examine high-income countries, drug quality concerns are by no means limited to less affluent nations, Ozawa said.
"Even in high-income countries, purchasing cheaper medicines from illegitimate sources online could result in obtaining substandard or falsified medicines," Ozawa said. "Verify the source before you buy medications, and make policymakers aware of the problem so they can work to improve the global supply chain of medicines."
The study wasn't a controlled experiment designed to prove whether or how counterfeit or poorly made medicines directly harm patients, however. And economic impact was difficult to assess from smaller studies that often didn't include detailed methodology for calculating the financial toll.
The report "provides important validation of what is largely already known," Tim Mackey of the Global Health Policy Institute in La Jolla, California, writes in an accompanying editorial.
"It is important to note that although the study is comprehensive, its narrow scope means it only provides a snapshot of the entire problem, as it is limited to studies conducted in low- and middle-income countries and to those medicines classified as essential by the World Health Organization."