Following a crackdown by elite drug squad officers the heroin market has been severely disrupted across Glasgow.
This has forced dealers to add legal highs, some of which are as deadly as hard drugs, to their supplies.
Graeme Pearson MSP, founder of the Scottish Drug Enforcement Agency, said mixing illegal drugs and legal highs is a "dangerous development".
He said: "Any new development is not good, but this is particularly worrying.
"Polypharmacy, as they call it in the trade, kills people.
"Abusing a number of different drugs - including alcohol - at the same time is very dangerous."
The heroin market has been severely disrupted after police made a series of high-value seizures.
We told last month how police smashed a £250,000 drugs ring suspected of selling heroin on city centre streets.
The Evening Times understands the drug is increasingly difficult to come by on the streets of Glasgow - forcing addicts to look for alternatives to feed their habit.
Our investigation reveals drug busts are up and Statement of Opinion Unit (STOP Unit) officers have seized heroin worth more than £3million in the past six months.
Seven men and three women - aged between 21 and 47 - were arrested last month in connection with alleged drugs offences during Operation Futa.
Detective Inspector Frank Clarke, who lead Futa, said: "Through this operation, we are targeting those who bring misery to our communities."
But deadly legal highs are becoming as dangerous as hard drugs, according to drug experts. A series of intelligence-led operations has made it more difficult for addicts to buy, and harder to find heroin of high purity, on sale from dealers.
Last month, drugs worth more than £1m were seized by police in Drumchapel.
Officers raided a property where they recovered the haul, thought to be heroin, cocaine, amphetamine and cannabis.
Two men, aged 46 and 47, were arrested in connection with the find.
In March, two men were arrested after £250,000 of heroin was recovered in Maryhill.
Just days earlier, another two men were arrested after drugs with a street value of £25,000 were found in a car in Glasgow's West End.
However, Scottish Drugs Forum (SDF) chiefs cast doubt over the impact of high-value drug seizures.
An SDF spokesman said: "Large, or high profile, police seizures do not necessarily lead to a change in the purity or composition of street heroin.
"Any such effect is likely to be very short-lived.
"Polydrug use - using more than one substance at a time - is a significant risk factor for overdose and death."