Doctors do not back plans to expand the prescription of heroin to addicts, a report concludes.
Over 400 patients are prescribed heroin
The Home Office wants heroin to be made available on prescription to all those who need it.
European studies have shown prescribing heroin has health and social benefits for long term drug users.
But researchers from the Joseph Rowntree Foundation said more UK research was needed to evaluate how beneficial it would be.
'Complex and patchy'
Around 2% of men and 1% of women in the UK report having tried heroin at some point in their lives.
Many do not become dependent users, but around 200,000 people are estimated to be currently living with heroin addiction - although experts say this figure is likely to be an underestimate.
Around 40,000 people are taking the heroin substitute methadone, but the treatment is not suitable for everyone.
The UK is one of the few countries where doctors can prescribe heroin, though few do so.
It is estimated that just 70 GPs are licensed to do so, but only 46 do so - to 448 patients.
The report from the Joseph Rowntree Foundation criticises the UK's services for drug users.
It says the pattern of provision is "complex and patchy", with a range of treatments being given in a variety of settings.
Only a small number of studies have been carried out in the UK, along with two larger studies in the Netherlands and Switzerland.
The studies suggest prescribing heroin can improve users physical and mental health and can reduce crime and illicit drug use,
But the report cautions there is no evidence regarding the impact of heroin prescribing on the community as a whole, and that the drug is more expensive to prescribe than methadone.
The report concludes: "A cautious assessment of the evidence suggests that heroin is potentially an effective treatment for some patients.
"The government's interest in expanding the provision of heroin prescribing provides the opportunity to do this.
"Any such expansion would need to be monitored and properly evaluated."
They say it would be a good opportunity to obtain conclusive evidence on the risks and benefits of heroin prescribing.
Professor Gerry Stimson, who co-wrote the report, said: "A cautious assessment of available evidence suggests that heroin is potentially effective as a treatment for some patients.
"But the unanswered questions include whether any benefits of prescribing heroin outweigh the additional costs.
"An expansion of heroin prescribing is generally welcome, but it must be accompanied by a rigorous, scientific evaluation of its value in treatment.
"It would be a failure of vision of, 10 years hence, we have the same, vague system in place and the same list of crucial questions about effectiveness waiting to be answered."
Dr Clare Gerada, spokeswoman on drugs for the Royal College of General Practitioners, said: "As we are still a long way from providing drug users with basic interventions such as methadone maintenance we need to see a greater investment in these services before committing to prescribing heroin on the NHS and creating addicts for life."