GLP-1 weight loss

How quickly you see results

GLP-1 medication works in phases. In the first 2-4 weeks you are on the starting dose (e.g. Mounjaro 2.5 mg, Wegovy 0.25 mg). That is a run-in period intended to build tolerance against side effects, not to lose weight. You often do feel a reduced appetite straight away, but the kilos only really start to come off from month 2.

From week 5 to week 16 you are in the active titration phase. The dose is increased every 4 weeks and weight loss accelerates. During this period you lose on average 1-2 kg per week with optimal treatment. That is more than the WHO guideline for responsible weight loss (0.5-1 kg/week) and sometimes causes 'Ozempic face' through rapid loss of facial volume.

After month 4-6 the pace stabilises. On the therapeutic maximum dose the effect continues, but the body adapts. The pace drops to 0.3-0.5 kg per week. After month 12 you are usually at or close to your new set point, and maintenance becomes more important than losing more.

Monthly figures per medicine

The following figures come from published clinical trials and are averages. Individual results vary between 50-150% of these values.

Saxenda (liraglutide 3 mg, daily injection): on average 1.5 kg per month in the first 6 months. After 56 weeks: on average 5-7% of starting weight (~6-8 kg for someone weighing 100 kg).

Ozempic (semaglutide 1 mg, weekly injection): on average 2 kg per month in the first 6 months. After 68 weeks: on average 10-12% of starting weight (~10-12 kg at 100 kg).

Wegovy (semaglutide 2.4 mg, weekly injection): on average 2.5-3 kg per month in the first 6 months. After 68 weeks: on average 15-17% of starting weight (~15-17 kg at 100 kg).

Mounjaro (tirzepatide 15 mg, weekly injection): on average 3-3.5 kg per month in the first 6 months. After 72 weeks: on average 18-22% of starting weight (~18-22 kg at 100 kg).

Rybelsus (semaglutide 14 mg, daily tablet): on average 1 kg per month. After 26 weeks: 5-8% of starting weight. Considerably less than the injectable forms because of lower absorption.

Factors that determine the pace

Five key factors make the difference between an 'average' result and an above-average or below-average result.

Starting weight: the higher the starting weight (and BMI), the more absolute kilos you lose. The percentage of weight loss, however, remains relatively constant. Someone weighing 130 kg loses more kilos over the same course than someone weighing 90 kg, but both end up with a comparable weight-loss percentage.

Dose: higher doses give more weight loss. Wegovy 1.7 mg gives ~10%, Wegovy 2.4 mg gives 15-17%. Sometimes a patient is already satisfied at 1.7 mg and the maximum dose does not need to be reached.

Diet and exercise: without lifestyle change, the effect roughly halves. Patients who also adjust their diet and do 150 min/week of moderate exercise achieve the top trial results. Patients who rely on medication alone achieve 5-8% instead of 15%.

Location of fat tissue: visceral obesity (around the abdomen) responds faster to GLP-1 than peripheral obesity (around the hips and thighs). Men therefore often lose measurable weight faster than women, although the percentage is ultimately comparable.

Medical co-factors: insulin resistance, thyroid dysfunction, hormonal imbalance (PCOS) and certain medication (antidepressants, antipsychotics, corticosteroids) slow the GLP-1 effect. In our programme this is monitored and, where necessary, treated alongside.

What to do when progress stalls

A stall after 3-6 months is very common and usually no cause for concern. As described, the pace naturally slows after month 4-6. A week or two without weight loss is normal.

Only after 4 consecutive weeks without weight loss, while you are still far from your goal, is action needed. Steps we go through: a diet review with a dietitian (calories often creep in through portion-size creep), stepping up exercise (adding strength training to preserve muscle mass), optimising the dose if you are not yet on the maximum, and possibly switching to a stronger medicine (e.g. from Ozempic to Mounjaro).

A specific form is the 'weight loss plateau' after 12-18 months: the body finds a new set point and the last 2-5% of weight loss comes slowly. This is medically and physically normal. Accepting the new body weight is often more important here than forcing out every last kilo.

First 6 weeks vs month 6

In the first 6 weeks you lose weight relatively quickly through three coinciding effects: drastically reduced appetite (especially in weeks 2-4), water loss from dietary changes, and depletion of glycogen stores. This is an 'artificially' fast start of 2-4 kg per week that settles down to the true rate of weight loss.

Months 2-4 are the real fat-burning phase. The pace is then 1-1.5 kg per week, mainly from fat tissue. This is the most sustainable and healthy weight loss.

Month 6 onwards is consolidation and metabolic adaptation. Basal metabolism drops slightly (on average 5-15% with substantial weight loss), the body becomes 'more economical' and has to work harder to keep losing weight. Protein intake (1.2-1.5 g/kg) and strength training become essential here to preserve muscle mass and limit the metabolic drop.

Maintaining weight loss

GLP-1 helps not only with losing weight but also with keeping it off. The STEP 4 trial showed that patients who continued Wegovy after 20 weeks maintained an average of 17% weight loss, while patients who were switched to placebo regained 7% of their weight over the same period.

This suggests that for many patients GLP-1 is a chronic therapy, just like blood pressure medication or statins. Stopping after reaching your target weight without replacement interventions (intensive coaching, lasting lifestyle change, possibly a 'maintenance' dose) often leads to most of the weight returning within 12-18 months.

At Go Leaner we therefore work with a 4-phase anti-yo-yo protocol: titration, weight loss, stabilisation and maintenance. In the maintenance phase the dose is sometimes halved and lifestyle coaching is intensified.

When are you a non-responder

The medical definition of non-response is less than 5% weight loss after 12 weeks on the therapeutic dose. That applies to around 8-15% of patients in trials.

Possible causes: too low a dose (solution: titrate to the maximum), too short a titration period (solution: patience, most of the result only comes at the maximum dose), interfering medication (antidepressants such as SSRIs or TCAs, antipsychotics, corticosteroids, certain anti-epileptics), undiagnosed hypothyroidism or cortisol overproduction (Cushing's), or an underlying eating disorder (e.g. binge eating) that GLP-1 does not resolve.

In the case of true non-response after 16-20 weeks on the maximum dose, you can switch to a different GLP-1. Switching from Ozempic to Wegovy (same substance, higher dose) is straightforward. Switching from semaglutide to tirzepatide (Mounjaro) often still produces a response because the dual mechanism activates different pathways.