A number of people have suffered side effects after receiving cosmetic injections, according to the UK Health Security Agency (UKHSA).
It said 14 people from County Durham and Darlington had experienced "adverse reactions" including eye drooping and double vision following the procedure involving "botulinum toxin" injections.
The organisation said 10 people had required treatment so far and it was advising clinicians in the area to look out for symptoms and reactions in people who had received similar injections recently.
Durham County Council official Amanda Healy said the authority was working with UKHSA to investigate the matter.
The health agency said its initial investigations suggested the issue was not due to contaminated products.
It said symptoms of botulism were being reported a few weeks after people had received the procedure and it had become aware of cases in the past few days.
'Counterfeit' suspicion
UKHSA official Dr Joanna Darke said: "Botulism is a rare infection, but it can be serious. It is caused by toxins produced by Clostridium botulinum bacteria.
"These toxins (but not the bacteria) are the active ingredient in Botox and similar products."
Allergan Aesthetics, the trademark owner and manufacturer of Botox, said it "is aware of recent reports of suspected botulism in patients in County Durham and Darlington who received injections of a product, being referred to as 'botox'".
"Investigations are ongoing and Allergan Aesthetics is working with the local authorities."
The company said it "suspects that the product administered is counterfeit, further underpinning the importance of ensuring you are acquiring a genuine product through reputable and trusted channels".
Dr Darke appealed for people who have recently had a procedure and are experiencing symptoms, such as slurred speech, to contact 111.
"There are effective treatments available," she said.
Ms Healy said aesthetic procedures were becoming more popular on the high street and people should ensure their practitioner wore PPE, washed their hands and carried out a pre-consultation.