Steve Collins is a 45-year-old unemployed architect who has been living with severe depression for 15 years. “I’m like a hermit crab hiding under rocks, crouching in dark spaces and only venturing out occasionally; there’s no light, no hope, no way in or out. I’ve been in therapy for years and must have taken at least six different antidepressant drugs. I had ECT (electroconvulsive therapy) and that literally shocked me out of it for a bit, but the depression came back – and the idea of ECT was so shocking for my family. People say: ‘Well, at least you haven’t got cancer.’ But, honestly, I’d rather have almost anything than live like this.”

A new type of treatment, vagal nerve stimulation (VNS), may offer hope for people like Collins who don’t improve with conventional depression treatment. A small battery-powered device like a pacemaker is inserted under the skin in the neck, from where it emits pulses of weak electical current to stimulate part of the vagus nerve. The vagus normally monitors our vital functions; it collects information about our breathing, heart rate and joint position, and sends signals back to the brain that tell it to respond if there are fluctuations.

No one fully understands how VNS works in severe depression that has been unresponsive to other treatments, admits psychiatrist Prof Hamish McAllister-Williams, of Newcastle University. “We don’t know exactly how lots of treatments work in psychiatry, including antidepressant drugs. I’m more interested in whether something works and, in the case of VNS, I’m persuaded that it does.” He cites two recent studies supporting the role of VNS, in addition to the usual treatment options of drugs, talking therapies and ECT. He says it’s likely to be a true effect, not just a placebo, because a placebo tends to kick in quickly – and wear off quickly – whereas VNS takes six months to work, but at least half of those who respond, remain well. It may be particularly effective with people like Collins, who have improved after ECT, but whose depression keeps on returning.

VNS is difficult to get in the UK; funding can only be arranged if the specialist appeals to a panel that funds individual requests. McAllister-Williams knows of some areas where funding has been agreed but it remains a postcode lottery. With each device costing about £10,000 and lasting 10 years, he believes it is cost-effective compared with regular ECT that costs £1,000 per treatment, or repeated hospital admissions. “I think VNS is being underused, especially among people who have responded to ECT but who have relapsed. And we know that if you wait for more than five years before offering the treatment, it’s less likely to work.”

But nothing that works is ever entirely free of side-effects, so what are the downsides? US psychiatrist Scott Aaronson is the lead author of a large, recently published five-year study, comparing the outcome for patients with treatment-resistant depression who are given standard treatment, with those given VNS. “The tolerability of the device is terrific. The main side-effect is hoarseness because the recurrent laryngeal nerve [that supplies the voice box] comes off the vagus nerve. Patients who want to sing in a choir or work in telemarketing may be bothered by the hoarseness – it sounds as if you’ve got a frog in your throat. But they can temporarily switch off the device by holding a magnet over it.”

Aaronson is also unsure about the exact way VNS works but says: “My best guess is that VNS stimulates the nerves that travel back up to the brain’s limbic system [the area that controls emotion, mood and behaviour] to release more neurotransmitters [chemical messengers between nerves]. We have animal models that show increased blood flow and neurotransmitters after VNS.” And he is convinced it is worth a try when all else has failed. “If I had severe depression and needed to feel better right away, I’d get ECT because VNS takes six months to kick in. But boy, every day, I’d rather have VNS than repeated ECT.”

Psychiatrist Umberto Albert, of the University of Turin, is also cautiously optimistic about VNS. “There is strong opposition to ECT in Italy, so we really don’t have anything to offer people with severe depression who have tried talking therapies and at least four antidepressant drugs. In the right patients, VNS can be effective, although they need to keep taking the drugs and be patient because it certainly takes six months until you see the effect.”

The mental health charity, Mind, remains cautious: “VNS can be used to treat severe, treatment-resistant depression but Nice has issued guidance saying that there is not much evidence about how well it works or how safe it is.” They also point to other side-effects including coughing, shortness of breath, changes to heart rhythm and worsening depression or mania. “For these reasons we would suggest that VNS should only ever be used as a last resort for treatment-resistant depression, when all other treatments have failed. Anyone considering VNS should be made fully aware of the procedure and the associated side-effects and be able to give full consent to treatment.”

For those – like Collins – for whom all other options have indeed been exhausted, the idea of a relatively low-risk gadget that boosts the body’s own chemicals, instead of relying on potentially toxic drugs, is certainly appealing. And this rapidly growing area of medicine called bioelectronics is being applied to a range of conditions. VNS is already approved by Nice to treat children with epilepsy who haven’t responded to standard treatments, and there is a lot of excitement about recently published work showing a positive effect in the treatment of rheumatoid arthritis and Crohn’s disease. So could these programmable implants one day replace medication? They are unlikely to be a panacea for all ills, but it certainly seems as if we’re going to be hearing a lot more about bioelectronics in the next few years.