GLP-1 prep guide.
What to do in the 7 days before your first dose.
A 90-day clinical timeline, a 7-step pre-dose checklist, what to actually expect in week 1, the dose-titration ladder, the red flags worth knowing, and the five things you should not do. Written for people about to start semaglutide or tirzepatide — branded, compounded, sublingual, or injectable.
The 90-day clinical timeline
GLP-1 medications (semaglutide, tirzepatide, liraglutide) take time. Knowing the timeline before you start saves a lot of false-quit decisions.
- Weeks 1–2: Appetite suppression starts within days, but at the starting dose (0.25mg for semaglutide), the effect is mild. Food noise quiets down. Most side effects (nausea, fatigue, constipation) peak here.
- Weeks 3–4: Dose escalates to 0.5mg. Side effects often briefly worsen, then settle. Weight loss may begin showing on the scale — typically 2–4 lbs in this window.
- Weeks 5–8: The body adapts. Side effects largely resolve for most patients. Weight loss continues at roughly 1–2 lbs per week for those responding well.
- Weeks 9–12: Dose typically escalates again (1.0mg semaglutide, 2.5–5mg tirzepatide). This is where many patients see meaningful, sustained weight loss begin. Trial data shows the median patient hits ~5% body-weight loss by week 12.
- Months 4–12: The maintenance dose holds. Cumulative loss for responders is typically 12–18% of body weight at the 12-month mark (semaglutide STEP trials) and 15–22% with tirzepatide (SURMOUNT trials).
7 days before your first dose
Get baseline labs (if your prescriber hasn't already ordered them).
CBC, comprehensive metabolic panel, HbA1c, lipid panel, fasting glucose. Optional but useful: thyroid panel (TSH), vitamin D, B12. Your prescriber may have already ordered these — if not, ask. Knowing your baseline lets you and your clinician evaluate the treatment objectively at 3 and 6 months.
Stock anti-nausea OTC supplies.
Ondansetron (Zofran) if your prescriber will prescribe one; otherwise: ginger chews, peppermint tea, electrolyte powders (LMNT, Liquid I.V., or generic). Bismuth subsalicylate (Pepto) for occasional indigestion. You will use these. Plan ahead so you're not searching at 11pm on dose night.
Plan your dose day.
Pick a consistent weekly day. Many patients pick Sunday evening so any side effects fall on the weekend. Set a phone reminder. Your dose will be roughly 24 hours of mild-to-moderate side effects, then settle.
Stock high-protein, low-volume foods.
Greek yogurt, cottage cheese, protein shakes, hard-boiled eggs, jerky, deli-style turkey. Why: appetite suppression means you'll eat less — protect protein intake or you'll lose muscle along with fat. Target 0.7–1g protein per pound of goal weight, daily.
Hydrate aggressively.
GLP-1s slow gastric emptying — dehydration is the most common preventable side effect. Target half your body weight in ounces of water daily, with electrolytes once a day. Black coffee and tea count; soda doesn't.
Add fiber.
Constipation is common in weeks 1–4. Psyllium husk (Metamucil), magnesium citrate, or just deliberately increase vegetables and beans. Start before your first dose; don't wait for the constipation to start.
Plan the dose-skip rule.
If your prescriber hasn't told you: if you forget a dose within 5 days of your scheduled day, take it as soon as you remember. If more than 5 days, skip and resume on your normal day. Never double-dose to catch up.
Week 1: what to actually expect
Day of dose (Sunday evening, in our example)
Inject (or place sublingually) on schedule. For the first 2–4 hours, you'll feel essentially nothing. Then within 6–12 hours, mild nausea often starts. Eat small, low-fat, low-sugar meals that night. Skip the high-fat take-out.
Day 1–2 post-dose
Most common side effects:
- Nausea — usually mild to moderate, peaks 24–36 hours post-dose. Hydration + ginger + small frequent meals beat it.
- Fatigue — you may feel slow, foggy, less motivated. This is normal and resolves within 48–72 hours of each dose.
- Reduced appetite — the point of the medication. Eat to a schedule (3 small meals + 1 snack), not to hunger, until your body learns the new rhythm.
- Constipation — may not start until day 3–4. Fiber + magnesium + water from day 1.
Day 3–7 post-dose
Side effects fade by day 3 for most patients. Appetite stays suppressed, which is what you want. Track weight (same time, same conditions) at the start of week 2 to see your baseline.
The dose-titration ladder
Most semaglutide and tirzepatide protocols follow a 4-week-per-step titration:
- Semaglutide: 0.25mg → 0.5mg → 1.0mg → 1.7mg → 2.4mg (each step held for 4 weeks before escalating)
- Tirzepatide: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
Side effects often briefly worsen at each step then settle within 1–2 weeks. Your prescriber may hold a step longer if side effects don't resolve. Don't push the schedule faster than your prescriber recommends — faster titration means worse side effects, not faster weight loss.
Red flags — when to call your prescriber
(or go to urgent care / ER if severe) if you experience:
- Severe, persistent abdominal pain that radiates to your back (potential pancreatitis)
- Vomiting that prevents you from keeping fluids down for more than 24 hours
- Vision changes (rare retinal side effect with rapid blood-glucose changes)
- A new lump or swelling in your neck (rare thyroid-related signal)
- Severe gallbladder symptoms — right-upper-quadrant pain after fatty meals
For routine side effects (mild-moderate nausea, fatigue, constipation, GI discomfort that's annoying but tolerable), message your prescriber via your provider's portal or app. They may adjust your titration or recommend symptom management.
What NOT to do
- Don't combine multiple GLP-1 medications. Some patients try stacking semaglutide + tirzepatide. Don't.
- Don't buy from "research peptide" sites. No quality control, no sterility, no dose accuracy. Save the money, use a licensed compounding pharmacy or branded medication.
- Don't quit on day 5 because the scale didn't move. The scale moves at weeks 3–4 minimum for most patients. Body-composition changes happen first.
- Don't skip protein when your appetite drops. Muscle loss is the single biggest preventable mistake on GLP-1s. Resistance training + protein protect lean mass.
- Don't drink alcohol the day of your dose. Compounds the nausea, dehydration, and GI discomfort.
What success looks like at 90 days
For an average patient who tolerates the medication well:
- 5–10% body-weight loss
- Side effects substantially resolved at the maintenance dose
- Habit-level changes: smaller portions feel normal, late-night cravings are mostly gone
- Lab improvements: HbA1c often down 0.3–0.7 points; fasting glucose normalized; lipid panel improving
- If you're not seeing scale progress at week 12 on a fully-titrated dose with good protein and hydration, talk to your prescriber about adjusting protocol
Where to go from here
If you haven't started your intake yet: browse the VYTAL.RX weight-loss programs or read our sublingual sema review and tirzepatide review for the deep-dive comparisons.
If you've already enrolled: bookmark this page. The 7-day prep checklist is most useful 3–4 days before your first dose arrives.
Not medical advice. This page is general and educational. Your specific protocol, side-effect risks, and dose timing should be reviewed by your licensed prescriber. Individual results may vary.