Increasing numbers of people are mixing heroin and crack together in what is known as 'speedballing'.
Drug users are mixing heroin and crack cocaine to make a 'speedball'
There are warnings that this risky process, which is becoming increasingly common, could lead to a rise in the numbers of drug users who die from an accidental overdose.
What is speedballing?
This is when heroin and crack are mixed in the same needle and injected together.
Why is it popular?
The sedative-stimulant combination creates what is said to be a "double hit". Heroin users also start taking crack to give them a lift, or "treat", while crack users begin using heroin to get a gentler come-down from their crack-induced high.
Taking both drugs in the same syringe therefore becomes a natural progression.
What are the risks involved with speedballing?
The main risk is overdosing, as the effect of each drug is harder to assess. Speedballers can use a bigger syringe and can also remain awake and not eat for three or four days.
Subsequently they cannot remember how much they have taken and may take an accidental, but fatal, overdose. The practice also increases the spread of Hepatitis B and C and HIV.
Speedballers will also inject between eight and 15 times a day, whereas heroin users will inject four to six times a day. Crack users can use their drug every 30 or 45 minutes.
Speedballers are also more likely to share needles, use contaminated equipment, inject directly into the artery, block veins and get deep vein thrombosis and abscesses.
Why has there been an increase in the use of speedballing? Where are the hotspots?
DrugScope's magazine Druglink conducted a survey of 20 towns and cities for its Street Drug Prices 2006 survey, with eight reporting a sharp increase in the practice over the last year.
These were Newcastle, Sheffield, Manchester, London, Bristol, Nottingham, Ipswich and York.
DrugScope says that research carried out on 100 drug addicts by Dr Russell Newcombe at Manchester drugs charity Lifeline
revealed speedballing was the main way to take drugs for 80% of those interviewed. The figure was 25% a decade ago.
Also, a series of studies of injecting drug users carried out in six areas by the Health Protection Agency found more than half of 1,000 needle exchange clients questioned in Wigan, Reading, Middlesbrough, Manchester, Bristol and Devon had injected a speedball.
What are the typical costs for users buying speedballs/crack/heroin on the street?
The average speedball is made up of £10 of heroin and £10 of crack. Most dealers sell the two drugs together as white (crack) and brown (heroin). In London this is known as "rice and curry". Some dealers give free crack away with two £10 bags of heroin.
What are the estimates about the costs surrounding those who speedball?
According to Druglink magazine, speedballers spend almost five times as much on drugs than heroin-only injectors - an average of £500 a week on drugs compared with £110 for heroin users.
They will also have three times as many criminal convictions as a heroin user, will be a more frequent injector and are more likely to share or re-use dirty needles.