Your first weeks on a GLP-1: what to expect

Stomach side effects are the most common early on

If you feel queasy in your first weeks, you’re seeing the most common pattern. The joint nutrition advisory from the American College of Lifestyle Medicine and partner societies notes that side effects are usually mild but show up most around starting and stepping up: “These are more likely to occur within the first weeks of initiation of therapy and with dose escalation.”³

Nausea is the symptom people report most, but it isn’t the only one. MedlinePlus lists nausea, vomiting, and diarrhea among the side effects that may occur with semaglutide, along with stomach pain, constipation, and heartburn or burping.¹ The tirzepatide page lists a similar set: nausea, vomiting, diarrhea, decreased appetite, constipation, and upset stomach.²

The advisory also describes a hopeful trend over time: “Side effects tend to decrease in frequency and severity with continuation of a stable dose.”³ This page describes what’s common — it isn’t medical advice. MedlinePlus’s instruction is to “tell your doctor if any of these symptoms are severe or do not go away.”¹

Appetite often changes

Many people notice they feel full sooner or think about food less. That lines up with how these medicines work. MedlinePlus describes semaglutide this way: “Semaglutide injection also slows the emptying of the stomach and may decrease appetite and cause weight loss,” and uses nearly identical wording for tirzepatide.^1,2

The joint nutrition advisory puts numbers to it: “Individuals using GLP-1s to treat obesity experience significant reductions in appetite and energy intake, with observed caloric reductions of 16-39%.”³ That’s a description of what researchers have observed across people, not a prediction for any one person.

It’s a weekly routine

These medicines are built around a once-a-week rhythm. MedlinePlus describes semaglutide as a solution in a prefilled pen injected under the skin, and states plainly: “It is injected once a week.”¹

Tirzepatide follows the same weekly cadence, with some flexibility in timing: “It is injected once a week with or without meals at any time of day.”² Settling into a consistent weekly habit is part of what the early weeks are about — the kind of thing a companion app like Tonic can help you keep in view.

What’s worth keeping an eye on

A descriptive picture of the early weeks points to a few things people commonly notice and may want to track: when stomach symptoms like nausea show up and how strong they are, since the advisory ties these to starting and dose changes³; shifts in appetite and how much you’re eating, given the documented reductions in appetite and energy intake³; and your weekly injection rhythm, since both medicines are once-weekly.^1,2

Tonic is a tracker and companion for noticing these patterns over time — it isn’t a medical provider and doesn’t make treatment decisions. For anything about your own dose or symptoms, MedlinePlus’s standing instruction applies: “tell your doctor if any of these symptoms are severe or do not go away.”¹