We think of opium poppies being grown in far off places like Afghanistan
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The government is considering whether legal, injectable heroin might be one way to tackle the effects of drug abuse, but where exactly do the authorities get their heroin from?
After a trial reported success in tackling use of street drugs and crime, Justice Secretary Jack Straw has suggested that prescribing heroin on the NHS may be the only way to deal with some users.
Most people probably think of opium poppies coming from Taliban-controlled fields in Afghanistan or from the Far East's Golden Triangle, but it is perfectly possible to produce opium in the UK.
Diamorphine for the addict treatment trial is produced in the UK
The UK has one diamorphine producer
Poppies are grown in Hampshire, Wiltshire and elsewhere in the south of England
Indeed, all of the diamorphine - equivalent to heroin - used in the UK's addict treatment trial is produced in the country.
Opiates firm Macfarlan Smith, a subsidiary of Johnson Matthey, is the country's sole diamorphine producer.
It holds contracts with farmers in the south of England - including Hampshire and Wiltshire - to grow crops of poppies, says Ian Godwin, communications director for Johnson Matthey. The firm takes the harvest and processes the poppies into what is called "active pharmaceutical ingredient" (API). This API is then passed on to a UK pharmaceuticals firm to be turned into doses.
The processing of opium poppies is done under government licence in "extremely secure" conditions.
The world's pharmaceutical firms get their poppies from everywhere from Spain to India, but the biggest producer is Tasmania in Australia. In Tasmania, a thousand farmers grow poppies across about 13,000 acres and it is one of the island's major exports.
The growing of poppies there can only be done under licence and there are strict controls on access to the field. Possession of opium poppies is a crime.
Heroin is not just for addicts but also for other medical uses
The heroin prescription trial in the UK, which is being run at the National Addiction Centre, initially used diamorphine imported specially from Switzerland and distinct from the NHS's own stockpile. It moved to using British diamorphine when that became a cheap enough option. The cost of a year's diamorphine treatment for an addict is about £15,000, although this includes administering and supervising the injections.
There have been similar trials involving pharmaceutical heroin in the Netherlands, Switzerland, Germany and Canada.
But the UK also has another use for diamorphine. It continues to be used in palliative care, to relieve pain in terminally ill people.
A recent problem with supply led to many doctors using other opioids, says Dr Bill Noble, president of the Association for Palliative Medicine.
"It is virtually the same as using morphine. The only difference is that diamorphine is much more soluble than morphine, which means you can have much lower volume injections."
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It is also used as part of the treatment for some patients with acute heart failure.
Diamorphine does not tend to be used in other countries for palliative purposes simply because it is illegal, says Dr Noble.