The risk of accidental heroin overdose through uncertain purity of illicit powders has long been an major hazard for users, with casual users most at risk, rather than dependent addicts who have developed tolerance to the drug effects.
Contrary to popular belief, heroin is rarely cut with impurities or diluting agents within the UK - average purities for police and customs seizures are similar, indicating most cutting to occur before importation, usually with other drugs such as paracetamol and caffeine
As an expert witness dealing with many drugs cases, I have encountered heroin purities as low as 4% and as high as 70%. Home Office statistics indicate average purity is falling - average purity may be related to climatic factors in producer countries - although low and high purity batches occur in all years. One of the lowest purity powders - an importation case - contained phenobarbitone, which could mask the low purity in the short term by putting the user to sleep. Although the market is unregulated, purveyors of sub-standard heroin could well expect to receive a visit from 'law of the jungle' enforcement agents armed with baseball bats!
The advice to users would be at first to try smaller quantities of Unknown heroin - this applies equally to all unknown drugs. Injecting users face the greatest risk as once in the drug cannot be taken out again, and unless prompt medical help is available death is a real possibility - particularly if using alone. Smokers and 'chasers' face lower overdose risk - once the user is unconscious no more drug would be inhaled - although the cost of use is greater.
One solution to the death toll might be to emulate the Swiss and make controlled doses of heroin (not just methadone) available to addicts on the NHS, with appropriate safeguards to avoid leakage to a 'grey market' while prescribing at levels sufficient to avoid users supplementing with street drugs. The cost of prescribable diamorphine is a fraction of the street price, and could be reduced further if agreement could be reached with producer countries to buy the raw opium at source. This would cut out the middle-men (i.e. drug traffickers & street dealers) completely by removing their suppliers, customers and income, and may stand a greater chance of success than current crop substitution and interdiction programmes. Unfortunately, the flaw in such a policy, and perhaps the real reason why it has never been adopted, may be fear of economic recession.
Many individuals (self included) and institutions who derive their income from the 'War on Drugs' would be put out of work. In addition, if users no longer need pay for their habits by stealing goods - usually replaced by insurance or otherwise - demand for consumer goods may fall sharply, bringing the wheels of industry to a halt.