Kenya's anti-drugs abuse agency, Nacada, has raised concern over drug addicts injecting themselves with animal tranquilisers as an alternative to heroin.

It follows the emergence of videos that have been shared widely on social media of people in the coastal region suspected to be drug abusers in “zombie-like” stances.

Nacada said in a statement on Sunday that it had not found in the samples it collected any presence of fentanyl - a deadly, synthetic opioid, many times more powerful than heroin - as was widely believed.

It found that the symptoms were due to a high dosage of heroin and a combination of heroin and other drugs including xylazine (a veterinary tranquiliser), prescription drugs and other substances.

Nacada said the abuse of the veterinary drugs “presents a potential public health crisis” in managing drug overdose cases.

“With the emerging evidence of non-medical use of veterinary drugs, there is urgent need to institute measures to regulate and control the diversion of such drugs into the illegal market,” it said in a statement.