FAKE medicines may cause poisoning and other harmful side effects, the World Health Organization (WHO) warned Sunday.

In a Facebook post, the WHO said taking fake medicines is fraught with health risks.

"These medicines won't treat or prevent disease and may cause harmful side effects. Only purchase medicines from authorized pharmacies," it said.

Fake and substandard drugs pose serious risks, as these often contain toxic levels of dangerous substances that can cause poisoning, said a National Institutes of Health (NIH) study.

The NIH said that fake drugs not only jeopardize public health but also pose a long-term threat by fueling drug resistance, endangering the well-being of communities worldwide.

WHO advised the public to buy medicines from authorized pharmacies and to consult healthcare providers immediately when concerns about medication arise.

The packaging must be inspected for signs of damage or tampering, it added.