Between January 2017 and December 2021, at least 605 tons of medical products were seized in West Africa during international operations, the United Nations Office on Drugs and Crime (UNODC) said, though reporting is inconsistent and the real number is likely to be higher.
Across sub-Saharan Africa, up to $44.7 million per year is spent on treating people who have used counterfeit or substandard malaria treatments, the report said.
And up to 267,000 deaths are linked each year to the use of substandard anti-malarials, according to World Health Organization data cited by the report.
Beyond the risk of counterfeits and poorly made drugs -- which at best do not work and at worst lead to toxic contaminations -- the report also warned of legitimate medications being used in unauthorized ways.
That can lead to increased resistance to frontline drugs such as antibiotics and anti-malarials.
"Once a (legitimate) product is diverted from the supply chain, there is very little (oversight) about how it is being used," said Francois Patuel, the head of the UNODC's Research and Awareness Unit.
"If you... ask for an antibiotic in the market, you will be able to purchase it. Whether it is the right antibiotic that should be used, or should be used at all, is not something that is controlled," he added.
"It is contributing to bacterial resistance and to antimalarial resistance."
The report, which focused specifically on trafficking within the Sahel countries of Mauritania, Mali, Burkina Faso, Niger and Chad, said the medical products that have been diverted from the legal supply chain typically come from Europe and to a lesser extent from China and India.
They often pass through seaports in Guinea, Ghana, Togo, Benin and Nigeria before being moved into the Sahel.
The financial benefits from the illicit trade are reaped by many, including pharmaceutical company employees, law enforcement officers and street vendors.
Armed groups, however, are less involved, it said.
"Despite terrorist groups and non-state armed groups being commonly associated with trafficking in medical products in the Sahel, most reported cases in the region show that the involvement of such groups is limited and mainly revolves around consuming medical products or levying 'taxes' on them in the areas under their control," it said.