One morning, I stood before my full-length mirror, scrutinizing the reflection of someone I thought I knew intimately—myself. Yet, ever since I began intermittently using the fat-loss medication Mounjaro in October 2024, my perception of my own body has become somewhat unclear.

At times, it feels as though my mirror has morphed into one of those whimsical funhouse mirrors, its surface distorting and altering my appearance in unpredictable ways. When I gaze at my reflection, I often perceive myself as larger, instinctively pulling in my stomach. Conversely, there are moments when I worry I’ve become too thin, fearing I appear gaunt or bird-like.

Despite being 59, I find myself struggling to view my body with any sort of clarity. My perception seems perpetually skewed, unable to accurately gauge my true size.

This personal struggle resonates with a broader trend reported by the NHS, which notes a surge in cases of body dysmorphic disorder (BDD). This condition causes individuals to fixate on perceived minor flaws or have unrealistic perceptions of their appearance. I can’t help but wonder how many people, like myself, who have used weight-loss injections, are experiencing similar distorted body images.

But the truth is, at the age of 59, I don’t seem to be able to look at myself with anything other than a distorted sense of my body’s actual size.

As the NHS reports rocketing levels of body dysmorphic disorder (BDD) – where sufferers obsess about trivial flaws or have wildly unrealistic ideas about what they look like – I wonder how many of these sufferers have been taking fat jabs like me.

Experts think social media, with its perfectly-­proportioned models and constant exhortation to ‘get the dream body’, is to blame for the large rise in referrals over the past three years. But could the increase in the use of GLP-1 medication also be changing our ability to properly judge how big (or small) we really are?

Granted, I’m not a great judge anyway. All my life I have ricocheted between a size ten and a size 16-18. At my heaviest, I was nearly 14 st and at that point surely suffered a reverse form of BDD.

I don’t seem to be able to look at myself with anything other than a distorted sense of my body’s actual size, writes Lucy Cavendish

Looking back, I was clearly overweight. My BMI was in the obese to near-morbidly obese scale, and I wonder at some of the clothes I squeezed myself into back then. The skinny jeans and tight dresses that revealed every one of my many extra pounds.

At that point I had grown to love my body. I told myself I was at peace with my weight. I was going to the gym and doing yoga, and I felt healthy. When I looked in the mirror I didn’t see a fat person. I saw myself – a woman who’d had four children and enjoyed her food and indeed her life. I had a little bit of padding, but I didn’t think I was big.

But, oh, I was big. My face was round and my tummy was spilling over every waistband. I have a photo of me in one dress where there were rolls and rolls of fat on me, yet I was quite happily strutting about, not in the slightest bit ­embarrassed. I look back at that now with a strange mixture of horror and pride.

In fact, when I look at photos of myself as a child, I see that I was chubby then too. My mother has sepia-tinted pictures of me sitting on a see-saw, aged about eight. My face is like a great big inflated balloon, and I’m wearing hotpant dungarees, the shorts of which are cutting horribly into my fat thighs. My tummy is protruding as if I’ve got a football under my T-shirt.

Yet back then, I saw myself as fairly normal. It took a few more years before I started understanding that I should be ashamed of my roundness. When I went into shops, I had to try on bigger jeans than my friends. If I wanted to get knee-high boots, I could never do the zips up because my calves were too big.

So I became obsessed with being slim and barely ate, and lost all sense of realistic body image. In my mid-teens, I was dangerously thin. But I remember quite clearly looking in the mirror and thinking I was fat, when actually I was Kate Moss-skinny.

In theory, fat jabs should stop all this – the relentless fluctuation of both weight and image. The idea is they help you get to a target weight and then you stay there. You’re grateful to have lost the muffin top, but you’re not so in thrall to diet ­culture that you carry on until you’ve almost disappeared. It was my doctor who suggested Mounjaro during a routine health check. Now I’m 4 st lighter and a size ten. I’ve spent a fortune on Mounjaro, and those clingy dresses and jeans fit perfectly.

And yet I don’t feel thin. Most of the time, I don’t think I look thin either. When people say things like, ‘Gosh you’re so slim’, I assume they’re talking about someone else.

Yes, I’ve lost all that flab, but my ability to see myself as I really am is no better than it ever was. It’s as though I’ve turned the ­telescope the right way round and now see myself magnified rather than shrunk. As though with each pound I’ve lost, my internal body image has recalibrated too, but upwards rather than down.

Why can’t we just relax into it all and accept ourselves?

I’m not the only one who has been on GLP-1 drugs who still can’t judge their size accurately. On TikTok a lot of people discuss their confusion when they look in the mirror, with some believing they’re ­terribly thin when they’re not, and others convinced they are larger than they should be despite large amounts of weight loss.

I’ve never lied about being on Mounjaro because I don’t want anyone to feel that I have lost 4 st by eating chia seeds and slaving away at the gym.

But perhaps the more sinister side-effects occur when you come off the jabs. So often we’re warned that you won’t stay slim when you stop the ­medication if your mindset hasn’t changed. But what if it’s changed too much? What if you’re ­constantly terrified you’re going to put it all back on again?

When people ask me how I’ve managed to keep the weight off the answer really is that I’m very strict about what I eat. I’ve decided that hunger is my friend. I do those things that I think supermodels do. If I want to eat, I drink water. If I still want to eat, I have an apple.

In my 20s, I’d tell myself that if I ate six biscuits, I’d skip lunch or dinner. Later on, pre-Mounjaro, I’d just eat the ­biscuits and not mind the extra wobble here and there. But now, I am ruthless: I will not eat a biscuit.

I scrutinise myself in the mirror with a forensic eye – and yet I still don’t entirely like, or understand, what I see. The mirror is still lying to me.

I don’t weigh myself, incidentally, because I’m terrified I’ll have put on weight and that any uptick will represent the beginning of a slippery slope back to 14 st. It never occurs to me that I’ll have lost weight. This is the psychological space most formerly large people inhabit. The thought of being underweight is impossible.

In many ways, being on weight-loss drugs has changed my life dramatically for the better: I feel lighter in every way. Yet my identity is still that of someone who is overweight. That internal Lucy is much more ­difficult to shift.

That’s why taking weight-loss drugs is like being in a hall of mirrors. People can tell me I look good. I can fit into size ten clothes. But in my mind I’m always assuming people are thinking: ‘What a big fatty.’ We can train our bodies, take drugs and eat nothing but two apples a day. Yet nothing stops the dysphoric thought process of the lifelong dieter-turned-fat jab user: what if everyone stays small and I get fat again?

It’s through that lens – with that fear – that I see myself when I look in the ­mirror. A thin woman who can’t believe her own eyes.