Side effects by week, and why the pattern repeats at every step

Every GLP-1 label spaces dose increases at least four weeks apart. The reason is pharmacology: a weekly dose takes four to five weeks to reach a steady level, and the gut takes about as long to get used to it. So the side effect curve below is not a month-one phenomenon. It restarts, usually smaller, at every step up.

Week 1 of a step

The first shot at a new dose is the one that bites. Nausea typically starts a day or two after the injection and is worst on days two and three. Appetite falls sharply, often further than it will settle. Some people have a day of fatigue or a headache. Diarrhoea, if it comes, is often in this week. Eating small and slow, and stopping early, is the whole strategy.

Week 2

The second shot lands on top of the first, so the drug level is higher than in week one, but the gut has started adapting. For most people week two is a little better than week one, not worse. Constipation can begin here as the slowed gut catches up. Reflux and belching are common. Appetite is still low.

Week 3

Noticeably easier for most. Nausea is now confined to a day or two after the shot, if it is there at all. The main complaints shift from the stomach to the bowels: constipation, bloating. Fibre and fluids do a lot here. Energy returns. This is also when weight usually starts moving if it is going to on this dose.

Week 4

Steady state. Side effects at week four are close to what this dose will feel like for as long as you stay on it. That is why the review happens here. If week four is tolerable and the dose is working, the prescriber may hold. If it is tolerable but weight has stalled, they may step up, and the curve begins again, usually gentler than the last time. If week four is still as rough as week one, the usual call is to hold, or to step back, rather than climb.

Beyond the ladder

Once you reach maintenance, the weekly rhythm is what is left: a slightly rougher day or two after the shot, then a flatter week. Over months, the things that creep in are different and slower. Hair shedding around month three to four, from the pace of weight loss. Muscle loss, if protein and training are not keeping up. Gallbladder symptoms, in a minority. The maintenance page covers what to watch over the long run.

When the pattern is not the pattern

Worsening after week two instead of improving. Vomiting most days. Pain rather than nausea. Constipation with a swollen abdomen. These are not the curve, and the right move is a call to your prescriber rather than waiting for the four-week review. The side effects page lists the red flags.

Seeing your own curve

This page describes the average. Your curve is in your log. A note on each dose with the day and severity, four weeks in a row, draws it for you, and the second dose step draws it again on top. In Peptide AI those notes sit on the same timeline as the dose, the food log and, on Premium, your weight and sleep from the watch. Two steps in, the pattern is unmistakable, and the four-week conversation gets much shorter.