Section one
What the trials actually found, what the labels actually say, and where the evidence is thinner than the confidence around it. Every claim links to its source.
Supplements
The shedding starts two to four months after the loss speeds up, which is why almost nobody connects the two. Seven supplements ranked — and one of them interferes with the blood test that rules out a heart attack.
Supplements
Bone is the tissue nobody thinks about until a wrist breaks. Rapid weight loss reduces bone mineral density, the effect is largest in exactly the people most likely to be prescribed these drugs, and none of it produces a symptom until it does.
Tools
I scored every tracker I could get my hands on against seven criteria that matter specifically on a GLP-1 — not generic calorie counting. Here is the ranking, the rubric behind it, and where my first choice falls short.
Supplements
You are already taking the most effective glucose-lowering drug most people will ever be prescribed. That changes what a supplement is for here — and it makes the hypoglycemia question the first one, not the last.
Mechanism
Semaglutide has a half-life of about a week. Tirzepatide's is about five days. Almost every practical question people ask me — the missed dose, the bad Tuesday, the surgery, the pregnancy — is a half-life question wearing a disguise.
Supplements
Start with the uncomfortable part: the face looks hollow because the fat in it is gone, and no supplement puts fat back. Seven products ranked anyway — honestly, with the evidence each one actually has.
Trackers
Retatrutide is a triple agonist still in phase 3 development, which means one of two things is true about anyone taking it: you are in a clinical trial, or you have bought something nobody has verified. The tracking advice differs sharply.
Supplements
A different question to which probiotic is best. When food volume halves, the bacteria that live on that food lose their substrate too — seven products ranked on whether they feed the microbiome or just add to it.
Supplements
The closest studied model for eating 800 calories a day is not dieting — it is bariatric surgery, where micronutrient monitoring is routine and nobody is embarrassed about taking a two-a-day. Seven multivitamins ranked on that logic.
Trackers
Whatever your GLP-1 arrives as, the four things worth logging are the same — and the two that decide your outcome are the ones people stop doing by month five. A tracking guide built around the treatment rather than the brand.
Access & Cost
List prices, direct-purchase programmes, what insurers actually deny and why, and how to write an appeal that works. Plus an analysis nobody publishes: what a percentage point of weight loss costs on each route.
Supplements
Skin that has been stretched for fifteen years does not spring back because you took collagen. Seven products ranked honestly, and a clear line between the laxity a supplement can touch and the kind only a surgeon can.
Supplements
Which magnesium salt you buy decides what the supplement does. On these drugs that choice inverts the usual advice — the poorly absorbed forms everyone warns you about are often the ones you want.
Supplements
Lifting is the single highest-value thing you can do on these drugs, and it is also the thing your appetite is actively working against. Seven products ranked for the specific problem of fuelling a session you do not want to eat for.
Trackers
An oral semaglutide tablet is a completely different tracking problem from a weekly injection: it is daily, it has a strict fasting window, and it will not work properly if you take it with anything else. Adherence stops being a reminder and becomes a protocol.
Getting Started
Most of the difference between a good outcome and a mediocre one is decided in the first three months, and almost nobody is given a plan. Here is the one I use — week by week, with the labs, the protein numbers, and what to track.
Supplements
Thirst goes quiet along with hunger, and about a fifth of your daily water used to arrive inside food you are no longer eating. Seven products ranked — and a clear line between the ones for an ordinary Tuesday and the one for a week with vomiting.
Supplements
The most common cause of light-headedness on these drugs is not a supplement deficiency. It is a blood pressure medication that was exactly right forty pounds ago. Read that part before you buy anything.
Supplements
The weakest-evidenced item in this series, ranked honestly. Probiotics work at the level of the strain, not the brand — and most of what is sold to GLP-1 users is a CFU number attached to bacteria nobody has studied for anything you have.
Trackers
One molecule, two brand names, and a set of tracking needs that follow the drug rather than the box. Plus the dose-escalation date almost nobody records, and why it matters if you take an oral contraceptive.
Supplements
Sleep changes on these drugs, and not only for the better. Seven products ranked — with a section on the two causes worth excluding first, because one of them improves as you lose weight and the other gets missed for years.
Trackers
Semaglutide reaches you as four different things — Ozempic, Wegovy, Rybelsus, or a compounded vial — and the tracking problem changes completely depending on which. Especially the vial.
Supplements
Nausea fades. Constipation tends not to. Seven fiber supplements ranked on the axis that actually matters when your stomach is already emptying slowly — how much gas they make on the way through.
Equipment
Every one of these estimates your body fat from how a small current travels through you, which means they are all measuring hydration as much as anything else. Seven ranked on the only thing they are actually good for — trend.
Evidence
I could not find a single place that laid out what each of these trials actually studied, in whom, for how long, and what it found. So I built one. Fourteen trials, compiled from the primary publications and kept current.
Equipment
If you take insulin or a sulfonylurea alongside a GLP-1, this is not optional equipment. Seven options ranked — and an honest section on whether a continuous monitor is worth it if you have no diabetes at all.
Side Effects
A triple agonist adds glucagon to the familiar two, and glucagon brings something the other drugs in this class do not: an effect on heart rate that trial protocols monitor and no consumer app will ever prompt you about.
Supplements
They arrive at two in the morning, in the calf, in month three. Seven products ranked — and a section on the two causes that are not a mineral shortfall at all, one of which is the statin you were already taking.
Nutrition
The powder you have to mix is the powder you skip on the morning you feel worst. Seven bottled shakes ranked on protein per 100 calories, lactose load, and whether they survive a day in a bag.
Side Effects
A daily GLP-1 pill that is not a peptide — which removes the fasting window that makes oral semaglutide so awkward, and keeps the gastrointestinal profile that defines the whole class.
Supplements
Cheap, boring, and among the best-evidenced supplements in existence — with two quirks that matter more on a GLP-1 than anywhere else: it makes the scale go up in week one, and it makes your creatinine look worse on a blood test.
Trackers
Zepbound is tirzepatide for obesity and, since 2024, for obstructive sleep apnea. If you were prescribed it for the second reason, the number that matters is not on your scale — and almost no app is built to record it.
Supplements
On 800 calories a day, protein stops being a preference and becomes arithmetic. Seven powders ranked on the two numbers that matter — protein per 100 calories, and leucine per scoop — plus whether you can still stand the taste in month four.
Supplements
Less common than constipation and more urgent when it happens. Seven products ranked — plus the two causes that look like drug side effects and are not, one of which follows the gallbladder trouble these drugs are known for.
Maintenance
The regain data is unambiguous and it is the conversation I want to have before the first injection, not after the thirteenth. On why 'chronic disease' is the operative phrase, and what a real exit plan looks like.
Side Effects
Delayed gastric emptying pushes stomach contents upward, which is why reflux that was occasional becomes nightly. Seven options ranked — and an argument for not settling into a proton pump inhibitor for two years without asking why.
Side Effects
The side-effect pattern of a GLP-1 is largely a property of the class, and most of what determines whether you get through the first three months is the same regardless of which one you were prescribed. Here is the part that generalises.
Supplements
The one supplement on this site with a firm rule attached: do not take it without a ferritin result. Seven ranked on elemental iron, and on the side effect that will make you stop — constipation, on a drug that already causes it.
Mental Health
The constant background negotiation about food goes silent, which is the relief people describe first. What arrives around month four is harder to name, and almost nobody is warned about it.
Supplements
The one supplement most likely to repeat on you when your stomach empties slowly, which is a shame, because it is also one of the better-evidenced things on the shelf. Seven ranked on EPA and DHA per capsule, and on freshness.
Trackers
Mounjaro is tirzepatide licensed for type 2 diabetes, which changes what you should be logging: glucose sits alongside dose, other diabetes medications need watching, and the oral contraceptive clock resets at every dose increase.
Supplements
Your appetite fell off a cliff. Your nutrient requirements did not. This is the short list of supplements that have an actual rationale on these drugs, the longer list that does not, and the tests worth doing before you buy anything.
Practical
There is no official conversion table between semaglutide and tirzepatide, which is the first thing to know — and the reason the most common switching mistake is starting too high.
Supplements
The one nutrient where guessing the dose is genuinely common and genuinely wrong in both directions. Seven ranked — and the case for testing before you buy any of them.
Side Effects
A dual agonist that produces the largest average weight loss in the class — which means more of everything, including the effects nobody warns you about. And one interaction whose clock restarts every single time you go up a dose.
Supplements
It peaks in the week after a dose increase and fades as you hold. Seven products ranked for that specific window — and an honest note that the most effective intervention is not a supplement at all, it is a slower titration.
Equipment
Your dose will need reducing as your weight falls, and the thing that lets a prescriber do that confidently is a week of readings from your kitchen table rather than one taken in a corridor.
Trackers
Wegovy comes as single-dose pens on a fixed five-step escalation, which makes the tracking problem different from Ozempic's: not how much is left in the pen, but how you tolerated each step — and whether you should take the next one.
Safety
The benefits are real and so is a risk that gets almost no attention: an older adult who loses 15% of their weight without a protein and training plan can arrive lighter, healthier on paper, and unable to get off the floor.
Side Effects
Tirzepatide at obesity doses, in a population that increasingly includes people treated for sleep apnea. Which raises a question the trials answer better than most people realise: what happens to daytime function while your gut is adjusting.
Safety
The contraindications are short, specific, and frequently skipped by a ten-minute online intake. The cautions are longer and more interesting. A screening guide written the way I would run it in clinic.
Equipment
A pen that freezes is a pen you throw away, and a hold can drop below freezing. Seven cases ranked on the only question that matters: how many hours of genuine 2–8°C they actually deliver.
Nutrition
A bar solves a problem a shake does not: it survives a handbag, a desk drawer and a day when you forgot to eat. Seven ranked on protein per bite, and on whether the sweetener wrecks an already unhappy gut.
Side Effects
Tirzepatide licensed for type 2 diabetes, which puts two things at the front that the obesity label does not: what happens when it meets your insulin, and a contraceptive interaction whose clock restarts every time you go up a dose.
Side Effects
An oral GLP-1 removes the injection and adds a variable nobody expects: how much drug you absorb depends on how you took the tablet. Which means an unpredictable week is often a dosing-conditions problem rather than a drug problem.
Monitoring
The scale answers a question you should mostly stop asking. Here is what DXA, bioimpedance, a tape measure and a set of photographs each actually tell you, and which one to spend money on.
Maintenance
The scale stops around month five and everyone assumes the drug quit working. Usually it did not. Here is how to tell a real plateau from a temporary one, and what is actually worth changing.
Trackers
Ozempic is a multi-dose pen, which creates a tracking problem the single-dose products don't have: four doses per pen, a dial you can misread, and a 56-day clock that starts the moment you use it.
Comorbidities
This is the off-label corner of the field. The rationale is real, the trials were mixed, and the risk that matters is one you can walk into by eating less: ketoacidosis with a glucose that looks fine.
Nutrition
Every piece of diet advice you have ever absorbed assumes eating less is the hard part. On this drug it is the easy part, and following that advice is how people end up at 700 calories with no muscle left.
Practical
Two things happen at once: most people find they want less of it, and most people find a smaller amount goes further. One of those is an interesting research finding. The other is how you end up unexpectedly drunk at a wedding.
Comorbidities
Hidradenitis suppurativa and psoriasis both track weight in ways most patients are never told about. If you have either, this is one of the more concrete reasons to be on this medication.
Practical
The rules are different for each product, they are not intuitive, and the one people get wrong is the gap after which you have to go back down rather than pick up where you left off.
Side Effects
Nausea gets all the attention. It is not usually what makes people quit. A practical field guide to the gastrointestinal reality, the genuinely serious risks, and the things that actually help.
Side Effects
One molecule, four delivery routes, and a side-effect profile that is largely the same across all of them — with one important exception. If your semaglutide comes from a compounded vial, the most likely serious problem is not the drug.
Comorbidities
Levothyroxine is dosed by body weight, which means your dose was calculated for a body you no longer have. Almost nobody rechecks, and the symptoms of getting it wrong look exactly like the drug working.
Practical
Nobody warns you that a drug for your metabolism can cost you enamel. The mechanisms are dull and entirely preventable, which is exactly why they are worth ten minutes of your attention.
Monitoring
Which markers to check before you start, at three months, and at a year — what each one is actually telling you, and the two that move early enough to be genuinely encouraging when the scale isn't.
Practical
Pens need refrigeration until they do not, security wants to see them, checked luggage will ruin them, and nobody tells you what to do about a seven-hour time difference on a weekly drug.
Comorbidities
Long-term weight loss lowers uric acid and reduces gout attacks. Getting there can provoke one, which is a genuinely unfair sequence and an entirely predictable one.
Practical
Nobody spends more than ninety seconds teaching this, and then you are alone in a bathroom with a pen. Sites, rotation, why a cold pen stings, and the two mistakes that waste doses.
Comorbidities
These are usually presented as rival answers to the same question. In practice they are increasingly used in sequence — and the combination that comes up most often is the one nobody planned for: regain, years after an operation.
Safety
A stomach that empties slowly can still hold food after a standard overnight fast, which is a problem under anaesthesia. The guidance has moved on from 'stop the drug' — but the instruction to you has not changed at all.
Cardiometabolic
Triglycerides fall a long way, HDL rises a little, and LDL barely moves — which surprises people who assumed losing weight fixes cholesterol. Here is what changes, what does not, and why your statin stays.
Side Effects
Wegovy titrates to 2.4 mg — the highest semaglutide dose in routine use — through five fixed steps. Which means the side-effect story here is really a story about escalation, and about the one decision you get to make five times.
Safety
Semaglutide is licensed from age twelve, the trial result was larger than in adults, and almost every conversation I have with parents about it is really a conversation about something else.
Practical
A stomach bug is a nuisance for most people. On this drug, with a diuretic and an ACE inhibitor still on board, it is the most common route to a hospital admission — and the plan takes ten minutes to agree in advance.
Side Effects
The nausea gets all the attention and is rarely what makes people quit. On Ozempic specifically the risk that deserves your attention is different: it is what happens when semaglutide meets the other diabetes drugs you are already taking.
Women's Health
The trials were not designed to answer the questions women actually ask me. Here is what we know about PCOS, contraception, fertility, and the perimenopausal years — and where the honest answer is still 'we don't know yet.'
Safety
Every one of these drugs delays gastric emptying — that is the mechanism, not a malfunction. The question worth answering is where the line sits between the intended effect and a condition you would not want.
Comorbidities
Two opposite things are true at once: these drugs protect the kidney over years, and they can injure it in a single bad week. Both belong in the same conversation and they almost never get one.
Safety
These drugs almost never cause a low on their own. Add insulin or a sulfonylurea and a much smaller plate, and they do — and the symptoms look enough like a dozen other things that people treat the wrong problem.
Comorbidities
Some of the most effective drugs in psychiatry cause substantial weight gain, and the people taking them are routinely told to eat less by clinicians who know perfectly well that is not what is happening.
Exercise
Lifting protects your muscle. It does not do the other job. Here is what cardio is actually for on this drug, why your resting heart rate went up, and how to train when you have not eaten enough to train.
Practical
Supply gaps are not an edge case in this drug class, they are a recurring feature. The damage is rarely the missed weeks themselves — it is what people do on either side of them.
Safety
A stomach that empties slowly changes how every pill you swallow is absorbed. Most of the time that does not matter. Here is the list of times it does — starting with the one on the tirzepatide label that almost nobody has read.
Cardiometabolic
Your blood pressure falls as your weight does, which is a benefit right up until the point where the dose set at your old weight becomes too much. Nobody schedules the review, and the symptom of missing it is a fall.
Safety
Two things are true and they point in opposite directions: obesity is a well-established cause of at least thirteen cancers, and these drugs carry a warning derived from tumours in rats. Here is how to hold both.
Cardiometabolic
SELECT was the trial that changed what these drugs are. A 20% reduction in major cardiovascular events, in people without diabetes — and a quiet argument about whether the benefit is really about weight at all.
Safety
Every one of these drugs carries a boxed warning about thyroid tumours, and it comes from rats. Whether it means anything for humans is a genuinely open question — here is what is known, what is not, and what to do with that.
Cardiometabolic
For years the advice to a breathless patient with a preserved ejection fraction was diuretics and a shrug. Two randomised trials have changed that, and the population they studied is a large share of the people reading this.
Comparisons
There is now a proper head-to-head trial, and it does show a winner on weight. Whether that makes it the right drug for you is a different question, and the trial cannot answer it.
Safety
Rapid weight loss makes gallstones. That was true long before these drugs existed, and it is the mechanism behind most of the gallbladder trouble people blame on the medication itself.
Safety
It appears in the warnings for every drug in this class and as a red flag on every page of this site. Here is what the evidence actually shows, and the one pattern of pain that should never wait until morning.
Comorbidities
Every extra kilogram lands on the knee several times over with each step, which is why the joint that hurts is usually the one carrying the most. There is now a randomised trial for this, and the result is better than most people expect.
Comorbidities
The commonest liver disease in the world has no approved drug for most of the people who have it, and a large share of them are sitting in front of a prescription that treats the thing causing it.
Comorbidities
Tirzepatide now carries an approved indication for obstructive sleep apnea, on the strength of a trial that cut the severity measure by about half. The practical consequence catches people out: your CPAP pressure is now wrong.
Body Composition
The scale is a terrible instrument for the thing you actually care about. What the body-composition data shows about lean mass on a GLP-1 — and the protein and training numbers I give every patient before their first injection.
Men's Health
Fat tissue converts testosterone into estradiol, which suppresses the signal to make more testosterone, which makes it easier to store fat. Losing weight interrupts that loop — and it does it better than a gel does.
Practical
A five-question online form and a pen in the post is not medical care. Here is what a good prescriber actually does, what the red flags look like, and the questions that separate them in about ninety seconds.
Evidence
The honest answer is four years for the newest agents and around a decade for the oldest, in trial populations that were watched closely. That is a lot more than nothing and a lot less than a lifetime.
Mechanism
Not an appetite suppressant. Not a stimulant. Not 'lazy Ozempic.' Here is the real mechanism, explained the way I explain it in the exam room when there is finally enough time.
Evidence
The gap between what a trial found and what the headline says about it is where most of the confusion in this field lives. Six things to check, in about the time it takes to read the press release.