Street drug ketamine should be offered as a last resort treatment for patients suffering from severe depression, scientists have said.
The horse tranquiliser, which is widely used as an illicit party substance, can be an "innovative" option for tackling the mental illness and should be explored by doctors, experts claimed.
In a paper for a leading science journal, co-authored by ex-drugs tsar Professor David Nutt, researchers said the use of ketamine for medical purposes "does not violate ethical practices".
Their call was met with caution by other leading scientists, who suggested more research was required before it could be recommended for widespread use.
The Oxford University-led paper based its recommendations on a study which gave more than 100 patients around 1,000 infusions of ketamine over the course of six years.
It found the drug could lead to rapid improvement in cases where all other avenues had been exhausted and had benefits lasting up to 14 days.
Dr Rupert McShane, a consultant psychiatrist at Oxford Health NHS Foundation Trust, said: "I have seen ketamine work where nothing has helped before.
"But ketamine is a drug not a miracle, and maintaining the benefit is a challenge. So far, the only way we have found to maintain the benefit is repeated dosing.
"We think that patients' treatment should be in specialist centres and formally tracked in national or international registries.
"This will help us to pick up any safety or abuse problems with longer term use, and narrow down what dose, frequency, route and duration of treatment works best."
Among a string of recommendations made in the paper, published in The Lancet Psychiatry, were that a national hub should be started to pool data from clinics using ketamine treatments.
It was also suggested guidance should be issued by professional bodies outlining the best means for using the drug as a treatment.
In 2014, ketamine was upgraded from Class C to B amid increasing concern over its physical and psychological effects.
There is evidence of users as young as 20 having their bladders removed due to heavy consumption of the drug.
Currently, doctors are able to give ketamine to patients "off label", meaning it is a licensed medication but being used for a purpose outside that for which it is marketed.
It is hoped by pooling data from off-label use and examining the results, further research can be carried out to mitigate the risks presented by using ketamine to treat severe depression.
The paper concluded: "We hope that the recommendations proposed here go some way to enabling innovative use of ketamine for treatment-resistant depression to continue, with appropriate care, precaution, and foresight."
One patient, David, who suffers from bipolar disorder, said: "Ketamine means that I can live for a few days a week rather than just exist but most importantly gives my wife back the man she married 40 years ago for those days.
"The ketamine doesn't have the unpleasant effects of other antidepressants, such as lithium tremor, or tiredness or nausea and I am fine to go home by train after two hours."
Professor Allan Young, chairman of the psychopharmacology special committee at the Royal College of Psychiatrists, said: "Despite clinical trials showing rapid improvement in mood after ketamine infusion, there are still significant gaps in our knowledge about dosage levels, treatment protocols and the effectiveness and safety of long term use.
"Before ketamine can be recommended for use in clinical practice, extensive research is required to understand how to optimally use ketamine for treating depression.
"The Royal College of Psychiatrists has concerns for patient safety; and hence recommends mental health practitioners to proceed with caution when treating patients with ketamine."