What happens in the first month on a GLP-1

The first month is the least representative month you will have. Understanding why saves a good deal of unnecessary worry in month two.

The starting dose is not the working dose

Semaglutide and tirzepatide are both started low and increased over a period of months. The starting dose exists to let your body tolerate the drug, not to produce weight loss. In STEP-1 the target dose was reached after 16 weeks of escalation.

So the first month tells you very little about how the medication will eventually work for you. People who conclude at week three that it is not working are usually judging a dose that was never intended to do the job.

Early loss is mostly water

Weight often drops quickly in the first two or three weeks, and most of that is not fat.

When food intake falls, the body uses stored glycogen. Glycogen is stored with several times its own weight in water, so depleting it produces a rapid drop on the scale that has nothing to do with fat loss. This is the same effect that makes low-carbohydrate diets look dramatic in week one.

Two consequences worth expecting:

• The fast start is not your rate. Do not extrapolate it. Applying week two’s rate to a year produces a number that will not happen.
• The slowdown in week four is not a plateau. It is the water finishing and the real rate appearing. This is the single most common cause of early discouragement.

The weight loss calculator shows what the trial populations actually did over 68 and 72 weeks, which is a more useful reference point than any early week.

Side effects, briefly

Nausea, reflux, constipation and fatigue are common early and usually ease as the body adapts. Eating smaller amounts more slowly helps most people. Anything severe, persistent, or that stops you eating or drinking properly is a call to your prescriber rather than something to push through.

We are not the right source for medical guidance on side effects, and this article will not pretend otherwise.

The thing actually worth doing in month one

Build the two habits now, while it is easy.

Protein. Appetite suppression is mild at the starting dose, which makes this the easiest month you will have to establish eating enough of it. Work out your target, count for three days once, and find two or three meals that reliably hit a third of it. Doing this at month one is straightforward. Doing it at month five, on a full dose with no appetite, is much harder.

Resistance training. Same logic. Two sessions a week established now becomes automatic. Started later, on lower energy, it often does not get started at all.

Neither of these will change much about month one. Both change a great deal about month twelve.

Take a starting measurement

If you have any access to a body-composition reading — a DEXA, or even a smart scale — take one now. A first reading is worth very little on its own, but it is the thing that makes every later reading meaningful, and it cannot be taken retrospectively.

This is the single most common regret people express about tracking on these medications: they started measuring after they had already lost 15 kg, and the most interesting comparison was gone.

If you have no reading, note your starting weight, your height, your age and roughly what you eat. The muscle check can work from those, and having the starting figure written down somewhere is worth more than it sounds.