drug users have been warned that the streets in Falkirk have been flooded with low-grade heroin.
And there are fears that it could lead to overdosing if purer substances are then used.
The problem was highlighted after 20 people were arrested during a police operation targeting heroin dealers.
Central Scotland officers recovered heroin with a street value of £3200 and £2000 in cash during Operation Innsbruck.
Houses in Stewart Road, Atholl Place, Victoria Road, Midthorn Crescent and Thornbridge Road, all in Falkirk, were raided, along with properties in Main Street, Bainsford, and Mansionhouse Road and Hamilton Street, Camelon.
Four men were also arrested in connection with supplying heroin in and around the area of the Castings Hostel in the Grahamston area.
Superintendent Robbie McGregor, Falkirk Area Commander, said: “This is our clear demonstration to our communities that we are listening and where there is evidence available we will act.”
Highlighting the problems associated with the strength of the drugs recovered, Detective Inspector Charlie Mitchell of the force’s drugs and organised crime unit said: “This operation revealed that the purity of the heroin being dealt at street level has changed dramatically in the last two years.
“Tests on £10 ‘street deals’ recovered showed that the purity levels ranged between one and 11 per cent with the drugs being heavily adulterated with a range of substances, not all of which have been identified.
“This dramatic change raises a number of issues. The adulterated drugs often lead to significant medical side effects and importantly it can reduce users’ drug tolerance which makes them dangerously vulnerable to overdose should there be a return to ‘normal’ purities.”
Dr Henry Prempeh, NHS Forth Valley’s consultant in public health medicine, said the dramatic change in purity raised a number of issues, including drugs ‘cut’ with other substances causing significant harm and resulting in side effects such as wound infections.