© Aaron Tilley and Kerry Hughes

At around nine o’clock every morning and evening, an alarm goes off on Barbara Nowak’s mobile phone. When she hears it, the 46-year-old geologist sits down at the kitchen table of her home in Sprockhövel, northern Germany, and takes a powerful cocktail of immunosuppressant drugs. Their names – tacrolimus, Mowel, prednisolone – are now woven into the fabric of her life. But today there’s a change to her daily routine. Before swallowing the pills, she pours herself a drink and downs it in one. It’s sweet, bitter, neon green – and tastes strongly of lavender.

In 1988, when she was 19 and studying for high-school exams, Nowak lost her kidneys to lupus. She has spent many exhausting years since on dialysis, sitting 12 hours a week at her local clinic with huge needles in her arm – her flesh is still gouged with scars. Receiving a donated kidney transformed her health. “It’s another life,” she says. She has energy again and can travel – she now takes part in geocaching challenges across Europe with her pet beagle. But there’s a downside. She’s dependent on twice-daily medication to suppress the immune responses that would destroy her transplant.

The drugs keep her kidney working but have side-effects, from tremors and nerve pain to gum disease and growth of facial hair. Nowak has been lucky enough so far to avoid the worst of these: although one drug started to destroy her red blood cells, since switching to an alternative she is dealing with her medication well. But she knows she is at increased risk of life-threatening infections, heart failure and cancer. And the drugs slowly poison the very organ she’s trying to save.

So Nowak is drinking this gaudy concoction as part of a pioneering trial at the nearby University of Essen. The “famous green drink” – as Schedlowski’s students like to call it – is an updated version of Marette’s rose and cod liver oil, invented to test conditioned responses in people. Like Ader, Schedlowski wanted something strange and unforgettable that stimulates several senses at once. He hit on strawberry milk mixed with green food colouring and essential oil. Its bright colour and overwhelming lavender flavour creates a bewildering mix of sensory cues, like drinking a violent, bittersweet battle between green and purple.

So far, Schedlowski has shown that after being associated with CsA, the drink reliably induces immunosuppression in healthy volunteers, creating on average 60–80 per cent of the effect of the drug. And just as in the rats, combining the conditioned response with a low drug dose prevents the learned association from fading. But will it work in patients?

I’m with Nowak on the trial’s last day. She is small but looks strong, and her tanned face is etched with smile lines. She says she was already familiar with the power of conditioning after using clicker training with her beagle, Ivy, and loved the idea of trying it on herself. “I thought it was so funny,” she says.

She removes her fleece to reveal a T-shirt with a stethoscope printed on it, then a research assistant hands her a 50-ml centrifuge tube, full to the brim with the green lavender milk. It’s the brightest thing in the room. “Danke schön!” she says. She gulps it fast, makes a face, and reaches into her rucksack for a sweet to take away the taste.

Schedlowski is running this trial with Oliver Witzke, a nephrologist at Essen’s University Hospital. For Witzke, the dangers of high drug doses are agonisingly real. He spends his career prescribing powerful immunosuppressants including CsA to kidney transplant recipients like Nowak. “Quite a lot of our patients die prematurely,” he says. “Not because the transplant fails… It’s due to the drugs that I prescribe every day.”

In every transplant patient he cares for, getting drug doses right is a delicate balancing act. Get the dose too low, and the patient will reject the kidney. But get it too high, and you’ll destroy the kidney or kill the patient. “We lose about 10 per cent of transplants in the first year,” says Witzke. Half of those patients go back on dialysis, the other half die. After that, the rate of decline slows, but some kidneys are still lost each year, and patients are at an increased risk of death due to drug complications.

One of the most damaging side-effects is nephrotoxicity: the drugs directly destroy kidney cells. The average life of a transplanted kidney is eight to ten years, says Witzke, and often when a kidney fails it isn’t clear whether the underlying cause is rejection or toxicity. “The dream for every transplant person is not to feed the patient from the first hour with a drug that’s toxic for the transplant.”

The search for immunosuppressants that aren’t nephrotoxic hasn’t been successful so far, but Witzke hopes that using conditioning to reduce doses will keep his patients alive longer. When he first heard about the concept, “I thought it was rubbish,” he admits. “As a doctor, I believe in pharmaceutics and drugs.” But Schedlowski’s experiments convinced him that the effect is not just a psychological trick. “It has a biochemical basis,” he says.

At this stage it’s too risky for Nowak and her fellow trial participants to reduce their drug doses, so the first step is to see if conditioning can suppress their immune systems over and above the effect of their normal pills. Some of the participants are taking CsA, but Nowak is on tacrolimus. In the learning phase of the study, she drank the lavender milk alongside her drugs, morning and evening, for three days. Then, after a two-day break, came the “evocation” phase, using the green drink to try to amplify the effect of her medication. She again downed the drink with her drugs, but this time, she drank it two extra times during the day, along with a placebo pill.

A pilot trial carried out in 2013 was promising: in all four patients, adding the green drink suppressed immune-cell proliferation and levels of the signalling molecule IL-2 by 20–40 per cent more than drugs alone. Now Nowak is part of a larger study of around 20 patients. If that works too, the next step will be to test whether this conditioned response can maintain immunosuppression while drug doses start to be reduced.

The hope is that this will reduce unwanted side-effects. Some problems, like infection risk, are likely to be an inevitable consequence of suppressing the immune system, whether that’s achieved using drugs or lavender milk. Others, like nausea, will perhaps be conditioned along with the immunosuppression. But Witzke argues that side-effects caused directly by drug toxicity – including kidney damage and increased cancer risk – are unlikely to accompany conditioned immune responses. It won’t be possible to lose the drugs completely, he says, but he hopes that even reducing doses by 20–30 per cent would improve quality of life while prolonging the survival of transplanted kidneys to perhaps 12 or 15 years.

Nowak isn’t convinced by the drink itself. “It’s awful!” she says. The taste got worse the more she drank, she explains, and she didn’t like carrying the odorous liquid around with her all day. An odd-tasting candy might be more practical and palatable, she suggests. But she’s right behind the principle of the trial, describing anything that might preserve her kidney as “very important”.

At 46, she is already on her third transplanted kidney. The first failed after a week, the second after 13 years – possibly because of drug toxicity – and her doctors say that after five years, her current kidney is ageing more quickly than expected. “It would be better if this one lasts longer,” she says bluntly. If it fails, she faces more years on risky, exhausting dialysis – average life expectancy on dialysis is just five to ten years – and the agonising wait for another donor.