"Hey doc, whaddaya reckon? Is this sore infected? Do I need antibiotics? Mind if I walk with you?"

So starts my clinical day as I walk from my parked car and potential patients fall in for street therapy. An informal consultation frequently ensues. Street drug users are in a hurry. Appointments and time management have no place in their chaotic lives. Setting aside time to see a doctor is well down the list of priorities. Most are in an endless rotating door — scamming at least a hundred dollars a day for heroin is the main game.

Informal street consults are the way I dispense medical advice to this marginalised group. Most have no GP and have never sat in a waiting room; nor are they likely to. Time is precious as they push the limits of endurance to survive on the streets. Tolerating this exotic clinical behaviour has given me access to an unusual underclass of patients who rarely see doctors at all.

I treat drug dependence within general practice in Kings Cross in Sydney. It is a magnet to drug users and is the epicentre of street drug culture in Australia — users flock here from all over the country. But first let me tell you what it is that makes the Cross different from anywhere else in Australia.

Demographically, Kings Cross is a village perched on a hill between Rushcutters Bay and Woolloomooloo with the highest population density in Australia. Few of its denizens travel by car, and so the streets are always full of people at all hours of the day and night. From its halcyon days as a place where actors, artists and writers lived to now, when drug users rub shoulders with yuppie designers, journalists and movie makers, the Cross has seen more than its share of eccentric and odd behaviour, holding, as it does, an edgy juxtaposition of the marginalised with the mainstream. If nothing else, the Cross and its habitués are tolerant of extreme diversity.

My practice is unique in that around half of my patients are injecting drug users. By the time they make it into treatment, a large proportion have depleted their finances and their health. Wasted, demoralised, often with criminal charges for break-and-enter or stealing hovering over their heads and the prospect of a jail sentence awaiting them, they attend my rooms. Their recent history is littered with failed attempts at home detoxification or geographical relocation to beat the heroin habit. Desperate family members will drag them in, trying to coerce them into treatment. This is rarely successful. Untreated serious infections are commonplace. Hepatitis C, chronic airways limitation, psychiatric comorbidity and serious injuries complicate their initial presentation.

For them, I facilitate treatment with pharmacotherapies like methadone, buprenorphine and naltrexone. These treatments fit well into a primary care setting, allowing users a window of sobriety, a chance to "chill out" and reassess their lives. However, none of these treatments is a panacea. Many will start treatment only to fall out and resume again at another time. Others manage to stick it out, putting up with the rigour of attending treatment centres to requalify as functioning members of society. There is a clear correlation between staying in treatment and improved outcomes in this population. But, for me, the most important thing is to establish a therapeutic alliance with these once-feral individuals — no matter how tenuous this may appear — and slowly, over time, to observe the re-integration of personality and lost talent. For many have rare gifts and capacities that have fallen into disuse over years of addiction. This process is among the most gratifying experiences in medicine that I can think of.

A psychiatrist once told me that treating addiction was the most difficult area of medicine to work in. I should adjust my expectations down from what I had been used to. In treating drug dependence, "there is no such thing as failure, just varying degrees of success", he said.

This adage has stuck with me over the years. It really means that any engagement with a drug user is a success of sorts, and that to keep them in treatment, even for a few weeks, may give them that glimmer of hope to revisit treatment options in the future.

In the past year I have had referrals from the nearby Medically Supervised Injection Centre. Some of these clients had never considered treatment as an option, but have had some gentle counselling in the "chill out room" after they have used their drug of choice. If they have experienced overdoses, there is some urgency in commencing treatment and I try to minimise the bureaucracy involved in providing them with a substitution treatment.

My guess is that my street consultations while I walk to coffee, lunch or back to my car in the evening will continue. Sometimes I will examine an abscess under a street light, listen to a wheeze on Darlinghurst Road and maybe get asked if I want to buy some marijuana by the 15-year-old kids who sell the stuff on the streets every night.

"Sorry doc, I didn't recognise you for a moment."