What You'll Learn
Table of Contents
Everything You Have Read Is An Average
“15% weight loss.” “Over 20% with tirzepatide.” Those numbers are correct and they are means. A mean tells you where the middle of a distribution sits; it tells you nothing about how wide the distribution is.
Both registration trials reported the spread, and it is rarely quoted. STEP-1, 1,961 adults, 68 weeks of weekly semaglutide 2.4 mg:
- 86.4% reached 5% loss or more — against 31.5% on placebo
- 69.1% reached 10% or more — against 12.0%
- 50.5% reached 15% or more — against 4.9%
Turn the first line around and you have the fact this article exists for: 13.6% of people taking the drug did not reach 5% loss. Roughly one in seven, over 68 weeks, in a monitored trial with lifestyle support attached.
And read the third line carefully. Half of the semaglutide group did not reach 15% — which is close to the figure most people have in their head as “what this drug does.”
1,047 of 1,211 participants (86.4%) on weekly semaglutide 2.4mg achieved 5% loss or more at week 68, against 31.5% on placebo. 50.5% reached 15% or more. The remainder is the group this page is about, and it is not small.
PMID: 33567185 ↗Dose And Time Explain A Lot Of It
SURMOUNT-1 randomised 2,539 adults to three different tirzepatide doses, which makes the dose effect visible in a way single-dose trials cannot:
- 5 mg: mean −15.0%, 85% reached 5% or more
- 10 mg: mean −19.5%, 89% reached 5% or more
- 15 mg: mean −20.9%, 91% reached 5% or more
- Placebo: mean −3.1%, 35% reached 5% or more
Two things follow. First, the dose you are on materially changes the expected result, and dose escalation is deliberately slow — SURMOUNT-1 included a 20-week escalation period before anyone was at their target dose. Second, both trials ran to 68 and 72 weeks. A great deal of the loss quoted in the headline figures accumulated in the second half of that.
If you are twelve weeks in and below target dose, you are not a non-responder. You are early. The month-by-month timeline shows what the trial curves actually did over that period.
Bottom line: Comparing week 12 of your own experience against a week-68 trial mean is the single most common way people conclude the drug has failed them. The comparison is not wrong by a little.
HealthRX — physician-supervised GLP-1 care
If you are genuinely not responding, the answer is usually a dose change or a switch to the other molecule. That is a clinical judgement about your case, and it needs someone who can make it.
See what the intake involves →Disclosure: we earn a commission if you start a plan through this link, at no extra cost to you. It does not change what this page says. HealthRX dispenses compounded semaglutide and tirzepatide, which are pharmacy-prepared formulations, not the FDA-approved branded products. Nothing on this page is medical advice — that is what the provider review is for.
The Scale Is One Instrument, And Not A Good One Alone
Before assuming nothing is happening, it is worth knowing what the scale can and cannot see.
Body weight is fat, lean tissue, bone, gut contents and water. Water alone moves several kilos across a week — with sodium intake, carbohydrate and glycogen, hormonal cycle, and constipation, which is itself a very common effect of these drugs. A flat scale over two weeks is inside normal noise.
There is a second reason, and it is the one this site exists for. Roughly a quarter to a third of the weight lost on these medications is lean mass. If you are eating enough protein and lifting, you are preserving more of that lean mass than a trial participant did — which means, for the same fat loss, your scale moves less.
That is a better outcome producing a worse-looking number. Waist circumference, how clothes fit, and progress in the gym are all reading something the scale is averaging away. Our muscle loss guide covers what the composition data actually shows.
What Is Worth Checking First
In rough order of how often each turns out to be the explanation:
1. Time and dose
Covered above. Escalation is slow by design, and the trials ran well over a year.
2. What is actually being eaten
Appetite suppression reduces intake — it does not set it. Liquid calories in particular pass under the satiety signal these drugs act on, because the mechanism works largely through gastric emptying and fullness. A few days of honest recording answers this faster than any theory.
3. Missed or mistimed doses
These are weekly injections and the schedule matters. This is a question for your prescriber, not for an article.
4. Injection technique and storage
Also a prescriber question, and a common enough one to be worth raising rather than assuming.
5. Other medications
Several widely prescribed drug classes are associated with weight gain and can work against the effect. Worth reviewing your full list with the person who prescribes it.
6. Untreated conditions
Thyroid function and other endocrine causes are standard things to check when weight will not move. Standard, and worth actually checking rather than assuming.
Important: Do not adjust your own dose, change the injection schedule, or add a second medication on the strength of anything you read online, here or elsewhere. Every item on this list that has an action attached is a conversation with your prescriber.
If It Genuinely Is Not Working
Sometimes, after the dose is at target and the time has passed and the food is accounted for, the answer is that this drug is not producing much in this person. That is what the 13.6% figure describes. It is a known outcome, it is in the registration trial, and it is not a personal failure.
What it is, is information for your clinician. The realistic options at that point — all of them theirs to raise, not yours to self-prescribe — include a different agent in the class, a different mechanism entirely, or reassessing whether something else is driving the weight.
One thing worth holding on to in the meantime: 5% loss, the threshold 13.6% did not clear, is itself a clinically meaningful number for metabolic risk. Progress that disappoints against a 20% headline is not the same as no progress. The cardiovascular trial ran in people who lost about 10%.
And the muscle question does not go away either way. Whatever the scale is doing, protein intake and resistance training are the levers that decide what kind of weight is leaving — and they work regardless of how well the drug is working.
