The first six weeks on GLP-1 therapy follow a fairly predictable arc. This is the realistic week-by-week version — not the social-media version.
Week 1: 0.25 mg semaglutide (or 2.5 mg tirzepatide)
Most patients feel essentially nothing the first three days. Day four through seven, two things often appear: mild nausea (especially after meals that include high-fat content) and a noticeable reduction in food noise. Weight change is typically 0–1 lb, and most of that is water from reduced carbohydrate intake.
Week 2
Side effects either stabilize or get slightly worse. The nausea-prone subset of patients (roughly 30%) will report constipation, occasional heartburn, and what's colloquially called "sulfur burps" — a side effect caused by delayed gastric emptying interacting with sulfur-containing foods. Mitigations are practical: smaller meals, more water, and avoiding very high-fat or very high-fiber meals close together.
Weeks 3–4: titration to 0.5 mg semaglutide (or 5 mg tirzepatide)
This is where most patients first feel the drug clearly. Appetite suppression is meaningful. Many patients report they have to remind themselves to eat. Weight loss accelerates — a typical range for weeks 3 and 4 combined is 3–6 lbs. Side effects may briefly worsen at the dose escalation point and then stabilize within a few days.
Weeks 5–6
By the end of week 6, most patients are 6–12 lbs down from baseline. The distribution is wide — high responders may be 15+ lbs down, and low responders may be 4 lbs down. This early variation is not strongly predictive of total response by month six.
Muscle mass at six weeks
Without resistance training, approximately 25–40% of weight lost in the first six weeks is lean mass. With resistance training plus adequate protein (1.6 g/kg body weight as a floor), that drops dramatically. This is the single most underemphasized intervention in the first six weeks. See our muscle preservation guide.
When to call your provider
- Persistent vomiting for more than 24 hours — especially without obvious cause
- Severe upper abdominal pain radiating to the back (rule out pancreatitis)
- Inability to keep fluids down — dehydration risk
- Symptoms of low blood sugar if you're also on insulin or sulfonylureas (combination dosing should be reviewed)
What to expect, summarized
Six weeks in, most patients are 6–12 lbs down, food noise is meaningfully reduced, and dose has stepped up to 0.5 mg semaglutide or 5 mg tirzepatide. Tolerance to GI side effects builds over the first 8–10 weeks. The biggest determinant of how the next six months look is whether resistance training and adequate protein are dialed in now.
NexLife scored highest on our rubric (94/100) for comprehensive GLP-1 care. Flat-rate pricing across full titration, labs included, MD/DO oversight, both 503A and 503B pharmacy partners.
This article was authored by Eduard Cristea and clinically reviewed by Dr. A. Goher, MD. Health Technology Researcher & Publisher. See our methodology and affiliate disclosure.