Last weekend I drove to Dorset to visit a friend.

As I paid for petrol near home I bought a coffee and then, because I’d skipped breakfast, grabbed a cinnamon pastry to eat in the car.

So far so normal.

Then ten miles down the road, somewhere around Southampton, the guilt kicked in. How many calories had I just consumed? How much fat, how much sugar? Could I have done without it (definitely, yes). So why didn’t I? Where was my self-control?

Reaching the edge of the New Forest, I pulled off the motorway and into a service station. As I rushed across the car park to find the toilets, another voice popped into my head. ‘Don’t do it. Just get back in the car.’ But I couldn’t.

Inside the cubicle, I pulled my hair back into a scrunchie, leant over the cistern and made myself sick. My shame felt complete. Who wants to throw up at all, let alone in a public toilet? And how on earth did it come to this? Why, at the age of 54, having never done this before, am I suddenly purging myself like a self-loathing teenager?

The answer, I’m reluctant to admit, lies with Mounjaro, the miracle weight-loss jab that everyone is hailing as a revolution in our fight against the flab.

I’ve been on it since the beginning of February and have lost 17kg – the equivalent of around two pounds a week.

While I was 78kg (12st 4lb) when I started, I’m now 61kg (9st 10lb) and in this respect I couldn’t be more delighted. I haven’t been this weight since before the birth of my fourth child, Dolly, in 2009.

It has been 16 years of watching the scales ominously creeping upwards, during which time I have been through perimenopause and then menopause. And it has taken just five incredible months to lose it all again. I can’t explain how amazing that feels.

Everyone is telling me how great I look, too.

The friend I visited in Dorset hugged me, saying, ‘I hardly recognise you,’ a comment which, with my warped logic, immediately vindicated the vomiting episode.

Another childhood friend said I looked like the ‘old’ Shona again. The Shona before running out of oestrogen and allowing the daily demands of motherhood to drive her to quaff and scoff pinot and Pringles every night.

I know there are people reading this who might be thinking ‘78kg? That’s not obese. You shouldn’t have qualified for a weight-loss jab.’ It’s a valid point.

But while my BMI wasn’t strictly over the threshold of 30 to pass the private pharmacy online assessment – at 28 it was slightly under – I figured it was close enough and, like everyone else I know, I simply tweaked the figures a little. I’m 5ft 7in, and 78kg felt fat on me.

In every photo I loathed myself. I looked like a frump with a double chin and excess rolls around my middle. But this isn’t an article about the justification for taking Mounjaro. There have already been plenty of those.

These weight-loss jabs – whether you agree with them or not – have given us post-menopausal women an ‘easy’, albeit expensive, way to shed unhealthy pounds and rediscover our figures again. Is it cheating? Who cares.

It’s undeniably healthier to be thinner. Evidence shows that being a healthy weight reduces the risk of heart disease, type 2 diabetes, high blood pressure and certain cancers. Plus, my energy levels are up, my knees no longer creak and I’m exercising regularly again.

So, what’s the problem?

The truth is unsettling and something I would never have predicted, but I can no longer ignore the darker side of what is happening to me. The fact is that using fat jabs has at the very least encouraged an unhealthy relationship with food, and at the very worst triggered an eating disorder.

If anyone had asked me at the beginning of this process, I would have said I had a pretty typical attitude towards food and body image. I enjoyed eating, but didn’t like the weight I put on as a result.

As a child and teenager, I was always naturally skinny. But I can recall how when, aged around 25, the scales hit nine stone, I felt mortified at how ‘heavy’ I was getting, though I’ve no memory of who I was comparing myself to.

Putting on weight in my 30s and 40s, through the births of four children, I tried to persuade myself that it didn’t matter if I was chubbier. I mean, who was looking at me anyway?

Before I knew it, I was an invisible married woman in my 50s and I came to realise that it’s a great pleasure in life to enjoy a delicious meal with a bottle of wine. If only it didn’t leave me looking – and feeling – lumpy, something I just couldn’t ignore.

My three daughters – aged between 15 and 26 – have a far healthier attitude and have versed me rigorously on Gen Z messaging.

Never, ever, mention weight. Never fat shame (even if you’re fat shaming yourself). It’s not about what you look like, it’s about eating healthily and loving your body, even if that body is podgy and your thighs are sticking together when you walk. Embrace your size, celebrate your shape.

Frankly, it’s been a bit like living in a Dove advert and it wasn’t enough to persuade me not to try the jabs.

But the thing about the Mounjaro effect is that you are compelled, daily, to appraise yourself physically. And for the first time in my life this has been a positive experience.

Instead of nit-picking over perceived flaws I’ve a new-found appreciation of what my body looks like when it’s slim. Whereas before I avoided mirrors like the plague, I now stand, starkers, in front of the full-length one in my bedroom marvelling at the fact I can see muscle definition on my thighs and one less roll of fat around my middle.

It feels a tad narcissistic but my body is wooing me in a way it has never done before. You might ask, so what? But this new-found vanity is having an insidious effect. The thinner I get, the higher I see the stakes becoming.

I jab once a week on a Sunday and eat minimally until Thursday. I’ve become like a Parisian woman waiting for the weekend before she allows herself food.

For four days I exist on 500 calories a day. While there are no universal recommendations when you’re using fat jabs, it’s generally considered women should be getting at least 1,200 calories daily, so I realise my intake is extremely low and unsustainable long term.

But I just don’t feel hungry. My stomach doesn’t rumble, and I don’t think about eating at all. But then, as the week progresses, the drug starts to wear off and hunger sets in. I’m walking past the fridge and thinking: ‘Mmm. Shall I eat a piece of cheese?’ It is suddenly so much harder to get to lunchtime without sustenance.

By the time Friday comes, I’m desperately repeating that Kate Moss mantra to myself: ‘Nothing tastes as good as skinny feels.’ The worst part is, I’m actually starting to believe this to be true.

This is the Mounjaro mind game nobody talks about. I now see food as the enemy, something to be avoided at all cost.

Another challenge is that my job as editor of a trade magazine takes me all over the world to conferences. I’m constantly moving through airports, checking in and out of hotels and trying to avoid the breakfast buffet.

It’s tricky at events like these to sit through dinners with work colleagues and not tuck in. Or to stick to water at the bar when everyone else is necking Negronis.

Around two months ago I started panicking, especially when I threw in the guilt around how much this was all costing me.

I’ve been paying between £150 and £180 a month for five months to receive Mounjaro depending on the dose. Total cost so far, £777.

It’s an eye-watering amount, even though I am saving somewhat on food and wine. But we already have huge financial outgoings as a family, and this investment in my weight loss is something I can’t afford to do without seeing results.

What’s the point of spending all this money if I am going to negate the effects by bingeing on a week’s worth of calories in a weekend or at a work function?

While grappling with all of this I fell upon the Apple TV drama, Physical, starring Rose Byrne as a tormented housewife in the 1980s. It might sound odd, but it was this series that first put the idea of purging into my head.

Rose is stick thin and battling the kind of demons that cause her to regularly buy several cheeseburgers from a drive-thru after the school run before checking herself into a motel room so she can eat them in private. She lines up these cheeseburgers on the bed like a ritual, wolfs them all down, then moves into the en suite to vomit them all up.

When I first watched this scene it was with a kind of horrified fascination. But then a niggling question kept popping into my head and it wouldn’t go away.

For the first time in my life, I wondered, ‘How hard is it to make yourself sick?’ So at the next conference I didn’t just push my food miserably around my plate pretending to take mouthfuls – I ate it enthusiastically, because now I had a plan. As soon as it was polite to do so, I escaped to the ladies to experiment with bringing it all up again.

The first time this happened I felt immediately disgusted with myself. I thought about my daughters and how concerned I would be if they were making themselves sick after eating.

But it’s scary how you can normalise something if you do it often enough. Now, even before I allow anything to pass my lips I’m already thinking: ‘It doesn’t matter. Just be sick afterwards.’ I’ve gone from vomiting up meals once or twice a week, to doing it whenever I feel I’ve eaten too much.

Five months into my ‘weight-loss journey’, I’m seriously concerned that I’m in the clutches of an eating disorder.

But am I alone in this?

So many women are now on Mounjaro, all of them hailing it as a miracle cure to midlife spread, but at what cost?

While many of us think of eating disorders as being the preserve of young women, experts have warned they are on the rise among women of my age – the group most drawn to weight-loss jabs.

Last month Dr Elizabeth Wassenaar, a specialist in the psychology of eating disorders, said that ‘up to 30 per cent of women in middle age may experience disordered eating symptoms’.

These weight-loss jabs are, quite rightly, prescribed for free on the NHS to those who are clinically obese or suffering from diabetes. Then there’s the rest of us: a swathe of desperate people prepared to pay because they think they’re fat or simply want to shift a stone or two.

How many like me, in this grey area, are vulnerable to getting an eating disorder or, worse, already have an underlying one which has driven them to work the system to get Mounjaro in the first place?

Yes, you have to pass an online consultation, but it’s a laughable box-ticking exercise in which you’re asked: ‘Have you ever suffered from anorexia or bulimia?’ I ticked ‘No’ (which was true, but nobody checked anyway).

Since I started buying Mounjaro in February they’ve tightened up the process. Now these private pharmacies must also insist on a video consultation before prescribing the jab.

But from people I’ve spoken to, even this is a formality and once you’re on their books, like me, it’s concerningly easy to keep renewing your order.

Last year, US doctor Tom Hildebrandt, who leads Mount Sinai’s Centre of Excellence in Eating and Weight Disorders in New York, warned that he was seeing an increase in patients with eating disorders taking weight-loss drugs. He said: ‘In some cases, a person’s brain may interpret such dramatic, sudden weight loss as starvation, making people more obsessive about food.

‘People who are taking these new weight-loss drugs may then find themselves compelled to further limit how much food they eat, even when it endangers their health.’

Other experts have called for studies into this unintended consequence, with one observing: ‘At the moment we don’t know what percentage of people taking the new class of weight-loss drugs are at risk of eating disorders because there are no published clinical trials addressing the question.’ It’s hugely concerning.

My family, meanwhile, are aware of my purging and have told me how worried they are about me. All three girls tell me I need to stop taking Mounjaro, stop making myself sick and get help.

My husband feels the same. He can see how much happier I am being slimmer but tells me I should be achieving these results by healthy exercise and a proper diet plan.

I’m just under my target weight of 10 stone now, which gives me a BMI of 21.1, smack bang in the middle of the ‘healthy weight’ category. I have one injection pen left and no need to carry on taking Mounjaro once that is used up.

I am also aware that by writing this article, I will quite probably be blacklisted from every online pharmacy in the country and never be able to buy it again. But I’m petrified that once I stop jabbing, the weight will pile back on.

And now I know what I’m capable of doing, it feels as if I’ve opened Pandora’s Box, unintentionally unleashing a whole host of other problems for myself.

I clearly need a plan and I owe it to my family to seek help and look after myself better.

My husband says he’ll drag me out on runs – oh, the joy – and my daughters keep nagging me to join them at the gym. But it won’t stop my fear of going back to how I was before. Mounjaro might be heralded as the new elixir of weight loss but it brings with it a huge emotional burden.

At the beginning of the year, I really thought I was investing in a better body image.

Little did I know that what I was actually buying was a slippery slope to bulimia.