GLP-1 Checklist Before Starting Your First Dose

The pen arrives in an insulated box, refrigerated, with a stack of paperwork most people don't read carefully. The instructions inside are clinically accurate but written for compliance rather than experience. What patients tend to want, in the days before that first injection, is the version of the information that addresses what the first month will actually feel like — and what small choices in the week ahead can make it easier.

Most of the answers exist in the published literature. They just aren't on the prescribing leaflet.

1. Where the pen lives in your kitchen

Unopened semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) pens require refrigeration between 36–46°F (2–8°C). The vegetable drawer is fine; the freezer compartment is not — these molecules denature at freezing temperatures and the pen becomes unusable. After first use, semaglutide pens can stay at room temperature (up to 86°F / 30°C) for 56 days; tirzepatide pens have a shorter room-temperature window of 21 days for the multi-dose presentations and should be returned to the fridge between weekly doses.

The practical implication is small but worth doing once: identify the fridge spot that is consistently cold, isn't near the door, and won't get jostled. Pens that slide and bend the needle hub waste the dose.

2. The injection itself takes longer than you expect

The recommended injection sites are the abdomen (avoiding the area within two inches of the navel), the front of the thigh, or the back of the upper arm. The needle is short and fine — most patients describe the sensation as a small pinch followed by no pain. The part that takes longer than the videos suggest is holding the pen in place after the click. For semaglutide, hold for at least six seconds; for tirzepatide, hold for five. Releasing too early leaves a portion of the dose on the skin.

Rotating sites week to week reduces local irritation and the rare lipohypertrophy (raised tissue at chronic injection sites) seen with insulin and occasionally with GLP-1s. The standard approach is to alternate sides of the same body region each week and rotate regions monthly.

The injection day choice that's actually important

Most patients pick the same day each week and don't think about it again. The choice worth making deliberately is the day of the week relative to your schedule. The first 24–48 hours after a dose increase are when glp-1/glp1-and-hydration-fatigue">nausea is most likely. Patients who inject Saturday morning often have an easier first week than those who inject Tuesday morning and need to be functional at work Wednesday. Sunday afternoons are also a common choice.

3. What to eat in the 48 hours before and after

The single most consistent piece of practical advice from obesity-medicine clinicians is to keep meals smaller, lower in fat, and free of carbonated drinks in the first 48 hours after a dose — especially during titration weeks when the dose increases. Slowed gastric emptying interacts poorly with greasy, fried, or large meals. Patients who follow the same intake pattern they had before tend to discover this empirically and unpleasantly.

Hydration is the other one. The medication reduces thirst signalling alongside hunger, and dehydration amplifies nausea, fatigue, and constipation — the three most common early side effects. Most clinicians recommend front-loading water intake during the day rather than relying on thirst as a cue.

For broader guidance on this, see our practical overview of what to eat on a GLP-1 and foods that tend to cause trouble.

4. Protein is no longer optional

Patients on GLP-1 medications tend to eat less. That part is the point. The complication is that reduced intake makes hitting protein targets considerably harder, and adequate protein is what determines how much of the weight loss comes from fat versus lean tissue. Jaime Linge's 2024 MRI sub-study of STEP 1 participants found that roughly 40% of total weight loss came from lean tissue when no specific protein intervention was applied.

Stuart Phillips at McMaster has consistently shown that protein intake in the 1.4–1.6 g/kg/day range supports muscle preservation during weight loss. For an 80-kg adult, that's 112–128 grams per day — a target that requires planning when total intake is suppressed. Putting protein at the start of each meal, before the fullness signal arrives, is the most reliable practical strategy.

The companion piece on building a high-protein meal plan on a GLP-1 covers concrete sample structures.

5. The first dose will probably feel like very little

Semaglutide starts at 0.25 mg weekly for four weeks before stepping up to 0.5 mg. Tirzepatide starts at 2.5 mg. These initial doses are subclinical for weight loss in most patients — they exist to let the GI system adapt to the medication. The first four weeks are titration, not treatment. Patients who expect rapid appetite suppression in week one and don't experience it sometimes assume the medication isn't working.

Meaningful appetite changes typically begin between weeks 4 and 8, as the dose climbs. The STEP 1 trial dosing schedule reaches the 2.4 mg maintenance dose at week 16. The full effect of any given dose develops over 4–6 weeks of steady-state administration. Patience in the first two months is partly biological.

6. Side effects follow a fairly predictable curve

Nausea is the most common, affecting roughly 40–50% of patients in the STEP trials, peaking in the days after each titration step and gradually subsiding as the body adapts to the new dose. Most cases are mild to moderate. Constipation affects 20–25%. Fatigue, especially in the first month, is also common and tends to resolve as appetite suppression stabilises and patients adjust eating patterns to ensure adequate intake.

Red-flag symptoms that warrant prompt clinical contact are severe abdominal pain (possible pancreatitis), persistent vomiting, jaundice, or new severe right-upper-quadrant pain (possible gallbladder issues). These are uncommon but recognised. Our piece on the side effects timeline week by week covers what tends to happen when.

The temperature problem with nausea

A practical tip rarely in the leaflet: cold or room-temperature foods often go down more easily during nausea windows than hot foods, partly because hot food aromas amplify the nausea response. Many patients shift toward yogurt, cottage cheese, cold deli protein, and smoothies during the first 48 hours after a dose increase.

7. The two-month assumption is worth setting

Whatever your weight goals, the realistic frame for the first two months is "see how the medication is working" — not "evaluate whether it's working." Trial data shows wide individual variation in early response: some patients lose meaningful weight in month one; others see most of the change beginning in month three or four. The dose isn't fully titrated until week 16 for semaglutide and week 20 for tirzepatide, and effect builds over additional weeks at each level.

Patients who weigh themselves daily during the titration period tend to find the variability disorienting. Most clinicians suggest weighing weekly at the same time of day, or focusing on changes in clothing fit, energy levels, and hunger patterns rather than the scale for the first 8–12 weeks.

8. Other medications and conditions worth flagging

Several interactions and conditions matter enough to mention to the prescribing clinician before starting. Oral medications with narrow therapeutic windows (warfarin, levothyroxine, some thyroid medications) may show altered absorption due to delayed gastric emptying. Oral contraceptives are typically still effective but the FDA prescribing information notes potential changes in absorption — backup contraception during the first month of tirzepatide is recommended specifically. Personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 is a contraindication. History of pancreatitis warrants discussion. Active gallbladder disease warrants discussion.

For patients with diabetes already on insulin or sulfonylureas, the dose of those medications typically needs to be reduced to prevent hypoglycemia. This is straightforward to manage but needs to be done at the start, not discovered through a low blood sugar episode.

For women specifically, our review of GLP-1 medications and women's hormones covers the contraceptive and reproductive considerations in more depth.