On a GLP-1? What Most People Learn After They Start

Thinking about a GLP-1, or already on one?

They work, and for some people they’re the most important medicine they’ll ever take. Here’s what being on one is really like, and what to plan for.

In the 2-year STEP 5 trial, 82% of people on semaglutide had at least one stomach side effect, versus 54% on placebo.

Key Insight:

↳ Stomach side effects are the main experience, and the main reason people stop.

↳ These drugs don’t block absorption. You eat less, so you get less, which is why deficiencies can show up.

↳ Right upper belly pain, especially after a fatty meal, is a call to your clinician, not something to wait out.

Why It Matters:

↳ Planning ahead for protein, muscle and a few nutrients can protect the results you’re working for.

↳ Knowing what’s normal, and what isn’t, makes it easier to stick with it if it’s right for you.

The Good:

↳ In the SELECT trial, semaglutide cut major heart events by 20% in people with overweight or obesity and heart disease, without diabetes.

↳ In real-world use at 1 year, people lost about 7.7% of their body weight on semaglutide and 12.4% on tirzepatide.

The Bad:

↳ In pooled data from 2,117 people over 68 weeks: nausea 43.9%, diarrhea 29.7%, vomiting 24.5% and constipation 24.2%.

↳ Burping, bloating, reflux and dry mouth catch a lot of people off guard.

↳ Most of it’s mild to moderate, and worst while the dose goes up. Nausea tends to peak around week 20, then eases.

↳ Weight regain after stopping is common.

The Ugly:

↳ A meta-analysis of randomized trials linked GLP-1 use to higher risk of gallbladder and bile duct disease, especially at higher doses, with longer use, and for weight loss.

↳ Fast weight loss and slower gallbladder emptying both promote stones, the same reason gallstones are common after weight loss surgery.

Why Deficiencies Show Up:

↳ In one claims-based study of adults with type 2 diabetes, about 22% of GLP-1 users got a new deficiency diagnosis within 12 months, most often vitamin D. Most of the authors worked for, or were paid by, a company that sells nutrition products.

↳ In trials, adults lost over 5 kg (about 11 lb) of lean mass after 68 weeks.

The Details:

↳ Get a baseline before you start: ferritin with CRP, B12, vitamin D, a metabolic panel, and a real count of your daily protein.

↳ Hit your protein target every day, and lift something twice per week.

↳ Retest at 6 and 12 months, when deficiencies tend to show up.

↳ Skip the GLP-1 branded vitamin packs. You need what you’re actually short on, measured.

↳ Hair shedding a few months in is usually a response to the weight loss itself, and it usually settles.

Why This Isn’t Everywhere:

↳ A prescription is written for what the drug does. Nutrition follow-up isn’t built into the prescribing workflow, and the side effect numbers live in trial tables most patients don’t see.

Why It’s a Win-Win I Wanted to Surface:

↳ You protect your muscle and your results.

↳ Your prescriber gets a baseline to compare against.

↳ Your household gets a plan instead of surprises.

We Actually Have a Book on This

Chapter 11 of The Root Cause of Your Symptoms, Uncovered has the full GLP-1 section, “The good, the bad, and the ugly,” with the tests to get and when.

Learn more about the book

Where the Numbers Come From

↳ STEP 5: Garvey et al., Nature Medicine, 2022. Pooled STEP 1 to 3: Wharton et al., 2022.

↳ SELECT: Lincoff et al., NEJM, 2023.

↳ Gallbladder risk: He et al., JAMA Internal Medicine, 2022.

↳ New deficiency diagnoses: Scott Butsch et al., Obesity Pillars, 2025, in adults with type 2 diabetes. Most authors were employed by or under contract with Abbott.

↳ Everything else: The Root Cause of Your Symptoms, Uncovered, 2nd edition, Chapter 11.

↳ Educational content. Keryn Gold holds a PhD in Biomedical Sciences, not a medical license. Not medical advice.

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If you could design your first 90 days on one, what would be on your plan?