The Skinny Jab Truth: A Doctor’s Honest Guide to GLP-1 Weight-Loss Medications (And the One Thing Nobody Tells You).
By Dr Mark Wilshere, NHS Doctor & Co-Founder of Dr Marks.
They’ve been called “miracle jabs,” “skinny pens” and the biggest shift in obesity medicine
in a generation. And for once, the hype isn’t entirely wrong, these drugs genuinely work.
But as an NHS doctor, I see the other side too: patients confused about which drug does
what, buying dubious pens off Instagram, and quietly running their bodies into nutritional
deficiency without realising it.
So let’s cut through the noise. Here’s what these medications actually are, how much weight you can realistically expect to lose, who can get them on the NHS, how to use them safely, and the one nutritional trap that catches almost everyone. Stick with me to the end: I’ve answered the questions I get asked most (“Do I inject forever?”, “What’s ‘Ozempic face’?”, “Can I drink alcohol?”) in a quick-fire FAQ, and there’s a section on who should never take these that could genuinely save someone from harm.
First, the name: what actually is a “GLP-1”?
GLP-1 stands for glucagon-like peptide-1, a hormone your gut naturally releases after you eat. It does three useful things: it tells your brain you’re full, it slows down how quickly your stomach empties, and it helps regulate blood sugar. The new generation of weight-loss drugs are lab-made versions (agonists) that switch on these same pathways, dialling down appetite and cravings.
The clever part is that the field has evolved from switching on one receptor to switching on
two, and soon, three.
The main players (and how much weight they shift)
Semaglutide — the original blockbuster (single agonist)
Semaglutide (brands: Wegovy for weight loss, Ozempic for diabetes, Rybelsus as a tablet)
activates the GLP-1 receptor alone.
- In the landmark trials, once-weekly injectable semaglutide 2.4 mg produced average
weight loss of around 15% of body weight over 68–72 weeks.
- A newer higher-dose (7.2 mg) study pushed this to roughly 21% at 72 weeks.
- The oral version has caught up impressively — the OASIS-4 trial of oral semaglutide 25
mg reported about 13.6% weight loss over 64 weeks.
Tirzepatide — the current NHS heavyweight (dual agonist)
Tirzepatide (brands: Mounjaro for weight and diabetes, Zepbound in the US) hits two
receptors, GLP-1 and GIP. That second receptor improves how the body handles insulin
and fat, and it translates into bigger numbers on the scales.
- In the SURMOUNT trials, tirzepatide delivered weight loss in the region of 13–21%
depending on dose.
- Crucially, the head-to-head SURMOUNT-5 trial (published in the New England Journal
of Medicine, 2025) compared the two directly: participants lost an average of 20.2% on
tirzepatide versus 13.7% on semaglutide over 72 weeks. That’s a meaningful gap and
it’s why tirzepatide is currently regarded as the most effective licensed option.
Oral options are arriving
The needle isn’t the only route anymore. Alongside oral semaglutide, orforglipron, a
once-daily GLP-1 pill, reported around 11.2% weight loss in its ATTAIN-1 phase 3 trial over
72 weeks. For people who can’t face injections, this is a genuine shift.
A note on real-world vs trial results: trial figures are the best-case scenario. Real
world data (Cleveland Clinic, 2025) shows people lose noticeably less, often because
they stop early or stay on low doses. Those who persist on higher maintenance doses
got closest to the trial numbers (around 18% for tirzepatide). Persistence and support
matter as much as the molecule.
Injection vs tablet — the quick comparison
The one on the horizon: retatrutide (the “triple G”)
If tirzepatide raised the bar, retatrutide (Eli Lilly, still investigational) may move it again. It’s
the first triple agonist, it activates GLP-1, GIP and a third receptor, glucagon.
Why does that third receptor matter? Glucagon-receptor activation increases the liver’s
ability to burn stored fat and boosts energy expenditure, a mechanism the GLP-1 and dual
drugs simply don’t have. In effect, it doesn’t just reduce what goes in; it helps ramp up
what’s burned.
Important — this is not yet available and is still in phase 3 trials. But the data so far is
striking:
- Phase 2 (NEJM, 2023): up to 24.2% weight loss at 48 weeks.
- Phase 3 TRIUMPH-4 (Dec 2025): up to 28.7% at 68 weeks.
- Phase 3 TRIUMPH-1 (May 2026): all doses met their targets, with the top dose reaching
around 30% in obesity without diabetes.
- It also showed dramatic reductions in liver fat in earlier studies.
Several more phase 3 readouts are due through 2026, and it isn’t licensed or on the market
yet. But it’s the drug to watch.
Can I get these on the NHS?
This is where there’s a lot of misunderstanding, so let me be precise.
NICE has approved tirzepatide (Mounjaro) for weight management, but access is
deliberately tightly controlled and rolled out in phases, prioritising those with the highest
clinical need first. As of the current phase, eligibility centres on:
- A BMI of 40 or above (with lower thresholds applied for people from South Asian,
Chinese, Middle Eastern, Black African and African-Caribbean backgrounds), plus
- Four or more weight-related health conditions (such as type 2 diabetes, high blood
pressure, high cholesterol, obstructive sleep apnoea or cardiovascular disease).
The criteria are being widened over time to include lower BMI bands, but the “highest need
first” principle still applies.
The crucial point about your GP
For weight loss, you generally cannot simply walk into your GP surgery and ask for a
private-style prescription on the NHS. NHS access for weight management runs through
commissioned weight-management pathways and specialist services, with
wraparound support from dieticians and other professionals, not ad-hoc GP prescribing
on request. In many areas patients are invited for assessment through a hub or service
rather than self-referring, and GP practices are not obliged to offer it (participation varies
by area and by practice).
So if you’re chasing these drugs purely for cosmetic weight loss and you don’t meet the
strict clinical criteria, the NHS route will very likely not be open to you, and that’s by
design, to direct a limited resource to those at greatest medical risk (For type 2 diabetes,
prescribing rules are separate and different).
Side effects — what to expect and how to reduce them
The side effects are broadly a class effect, similar across all these drugs, and mostly
gastrointestinal. The commonest are nausea, constipation or diarrhoea, reflux, bloating, and
occasionally vomiting. They’re usually mild-to-moderate and worst during dose
escalation, settling as your body adjusts.
More serious but rarer issues include gallbladder problems and pancreatitis, which is why
medical supervision matters.
My top tips to reduce side effects:
1. Go low and slow. Most side effects come from titrating up too fast. Don’t rush to the
top dose.
2. Eat smaller portions. Your stomach empties more slowly now, large meals are the
fast track to nausea.
3. Prioritise protein and stay hydrated. This helps nausea and protects muscle (more on
that below).
4. Avoid greasy, fatty and very spicy foods, especially in the first days after a dose
increase.
5. Don’t lie down straight after eating if reflux is an issue.
6. Stay ahead of constipation with fibre, fluids and movement; ask your prescriber about
a gentle laxative if needed.
7. Report severe or persistent vomiting, prolonged vomiting risks dehydration and,
rarely, serious thiamine (vitamin B1) depletion.
Who should NOT take these medications
This is the section I most want people to read, because it’s the one that gets skipped, and
it’s exactly what a back-street seller will never ask you about. These drugs are powerful, and
they aren’t right for everyone.
Do not take these if you:
- Have a personal or family history of medullary thyroid cancer (MTC) or Multiple
Endocrine Neoplasia syndrome type 2 (MEN2), this is a specific, serious warning on
the labelling.
- Have had pancreatitis, or develop severe, persistent abdominal pain while taking
them (stop and seek urgent advice).
- Are pregnant, trying for a baby, or breastfeeding. These should be stopped well
before a planned pregnancy. Note too that tirzepatide can reduce the absorption of the
oral contraceptive pill, so a backup or non-oral method may be needed.
- Have a known serious allergy to the medication or its ingredients.
Speak to your prescriber carefully first if you:
- Have a history of gallbladder disease or gallstones (rapid weight loss increases the
risk).
- Have diabetic eye disease (retinopathy), rapid changes in blood sugar can worsen
it.
- Have a current or past eating disorder, appetite-suppressing medication carries real
risks here and needs specialist oversight.
- Have severe gut conditions such as gastroparesis, or significant kidney or liver
problems.
- Take insulin or sulfonylureas for diabetes, doses often need adjusting to avoid
hypoglycaemia.
If any of these apply to you, it doesn’t necessarily mean these drugs are off the table forever, it means the decision needs a proper clinical conversation, not a click on a website.
Buying privately: the safe way vs the dangerous way
These medications can be bought privately in the UK, legitimately, through regulated
pharmacies and reputable online providers with a proper clinical consultation and a
prescription. That’s a valid route for people who don’t meet NHS criteria.
But here’s where I have to put my doctor’s hat on firmly.
Do not buy weight-loss injections from social media, Facebook groups, unregulated
websites or “beauty” resellers. The risks are real and serious:
- You have no idea what’s in the pen. Counterfeit and black-market products may
contain the wrong dose, a different substance entirely, or nothing active at all. There
have been confirmed cases of fake pens causing harm.
- No clinical assessment means no one is checking whether the drug is safe for you,
contraindications like a personal/family history of certain thyroid cancers or pancreatitis
get missed.
- No monitoring, no follow-up, no recourse if something goes wrong.
- Sterility and storage can’t be guaranteed, these are injectables that require cold
chain handling.
If it’s cheaper than every registered pharmacy and it’s being sold through a DM, assume it’s
not what it claims to be. A regulated prescriber and a registered pharmacy are non
negotiable.
The bit nobody warns you about: the nutritional risk
Here’s the part that, as both a doctor and someone who formulates supplements, I care
about most, because it’s the most overlooked.
These drugs work by making you eat less. That’s the point. But when your total food intake
drops sharply, your intake of vitamins, minerals and protein drops with it, even if the
number on the scales looks perfect. You can lose weight beautifully and become
nutritionally depleted at the same time.
The evidence is now hard to ignore:
- A narrative review in Clinical Obesity (2026) pooling data across large cohorts found
vitamin D deficiency was the most common problem, affecting around 7.5% at 6
months and 13.6% at 12 months, alongside frequent iron depletion (GLP-1 users
had 26–30% lower ferritin than comparators). More than 60% were consuming below
their requirements for calcium and iron.
- A large US database study found 12.7% of people on GLP-1s were newly diagnosed
with a nutritional deficiency by 6 months, rising to around 22% by 12 months, and
the deficits worsened the longer people stayed on treatment.
- Commonly affected nutrients include vitamin D, iron, vitamin B12, thiamine (B1),
folate, calcium, zinc and protein.
- Muscle matters too. A portion of the weight lost is lean tissue, not just fat, some
studies suggest a meaningful share of total weight lost can come from muscle. Losing
muscle harms metabolism, strength and long-term weight maintenance.
Researchers reviewing this data have explicitly noted that multivitamin supplementation
is a sensible, evidence-aligned way to cover these gaps while intake is reduced, and
there are currently no formal micronutrient monitoring guidelines for GLP-1 users the
way there are after bariatric surgery, which means the responsibility often falls to the patient to be proactive.
Why I’d recommend a quality multivitamin alongside these drugs
This is exactly the scenario a well-formulated daily multivitamin is built for. When you’re
eating a fraction of your usual food, a clean, comprehensive multivitamin, covering
vitamin D, B12, B1, folate, iron, zinc and calcium, acts as a nutritional safety net so that fat is what you lose, not your bone density, energy or immune resilience.
Our Dr Marks Multivitamin and Dr Marks Over 50s Multivitamin were formulated with
doctor-led, clean-ingredient principles precisely for people whose intake or absorption is
compromised, and the over-50s formula is especially relevant here, because B12
absorption and bone health are already bigger concerns with age, and this generation of
medications adds to that load.
Pair it with protein. Alongside a multivitamin, keeping protein intake up (aim for protein at every meal, even small ones) is the single best thing you can do to protect muscle while you lose fat. Supplements support your micronutrients; protein protects your frame.
Your questions, answered
Do I have to inject forever? Obesity is a chronic condition, and these drugs manage it
rather than cure it. Trials consistently show significant weight regain once the medication
stops, in some studies people regained much of what they’d lost within a year. Think of it
as long-term treatment, not a short course. Some people step down to a lower maintenance dose; that’s a conversation for your prescriber.
What is “Ozempic face”? It’s the gaunt, hollowed look that can follow rapid weight loss,
you lose facial fat and, if you’re not careful, the muscle and collagen support underneath. It
isn’t really a drug side effect; it’s a rapid-weight-loss and under-nutrition effect. Losing
weight more gradually, keeping protein high, and covering your micronutrients (which
support skin, collagen and muscle) all help.
Can I drink alcohol? There’s no absolute ban, but many people find their desire for alcohol
drops anyway. Alcohol can worsen nausea, adds empty calories, and irritates the stomach,
so moderation is sensible, especially early on.
Will I lose muscle as well as fat? Some of the weight lost is lean tissue, not just fat. That’s
why protein at every meal and regular strength/resistance exercise matter so much, they
protect the muscle that keeps your metabolism and strength up.
What if I miss a dose? For weekly injections, most products allow you to take it within a few days of the missed dose, then resume your usual schedule, but always follow your specific product’s instructions or ask your pharmacist.
Can I get these just to slim down for a holiday or wedding? Honestly, these aren’t
cosmetic quick-fixes, and because the weight tends to return when you stop, using them
that way misses the point. They’re for meaningful, clinically-indicated weight management
under proper supervision.
The bottom line
GLP-1, dual and (soon) triple agonist medications are a genuine breakthrough, with
tirzepatide leading the licensed pack, semaglutide close behind, oral options arriving, and
retatrutide’s phase 3 data hinting at something even more powerful to come. Used properly, under medical supervision, from a regulated source, they can be life-changing.
But they are a tool, not magic. Get them from a legitimate prescriber, never from social
media. Manage the side effects sensibly. And don’t fall into the trap of losing weight while
losing your health, protect your nutrition and your muscle every step of the way.
Your future self will thank you for doing it properly.
(Dr Mark Wilshere is an NHS doctor and a co-founder of Dr Marks, a doctor-formulated
supplement range built on clean, evidence-led ingredients. This article is general
information and education, not personal medical advice, always consult a qualified
clinician before starting, stopping or changing any medication).
