Dr. William Yi
OrderlyMeds Medical Expert
GLP-1 Side Effects 101: this is the resource patients ask for most — and the one to come back to every time a new symptom shows up. Most of what people experience isn’t a sign something has gone wrong. It’s a direct result of how these medications work. This guide covers every GLP-1 side effect and exactly how to manage each one.
In this webinar, Dr. William Yi — a board-certified general and bariatric surgeon — walks through every significant GLP-1 side effect, explains the reason behind each one, and gives specific strategies to manage them. Whether you’re just starting out or a few months in, this is the resource to come back to.
GLP-1 medications slow down your digestive system. That single mechanism — delayed gastric emptying — is responsible for most side effects people experience: nausea, constipation, diarrhea, and heartburn. It’s also what makes you feel full and drives weight loss.
The important thing to know: most GLP-1 side effects are manageable, temporary, and predictable. Hair loss is reversible with proper protein intake. Fatigue improves with hydration and nutrition. Nausea typically resolves by week five. Food noise decreases as the medication reaches therapeutic levels. Understanding why these things happen makes them significantly easier to deal with.
The strategies below come directly from Dr. Yi — and they’re the same ones he uses with his bariatric surgery patients.
Meet The Expert
Dr. William Yi, MD Board-certified general surgeon specializing in general and bariatric surgery, practicing in Northeastern Pennsylvania (Scranton/Wilkes-Barre area). Dr. Yi trained at Vanderbilt University School of Medicine and completed his residency at Georgetown University. He has extensive clinical experience prescribing and managing GLP-1 medications alongside bariatric surgical care. He grew up personally navigating weight challenges, giving him both a clinical and lived perspective on this topic.
GLP-1 Side Effects 101: Why They Happen
Almost every GLP-1 side effect comes from one mechanism: these medications slow your digestive system down. GLP-1 medications mimic hormones your body already produces. When you take them, they signal your stomach and intestines to slow down — a process called delayed gastric emptying. This is exactly what makes you feel full, eat less, and lose weight. But that same mechanism also causes nausea, constipation, and heartburn.
In other words, side effects and results come from the same source. When side effects show up, the medication is working. The question is how to manage them well.
“The principal side effect is constipation,” Dr. Yi explains, “because the same effect that makes you feel full also slows the gut. These aren’t signs something has gone wrong — they’re a consequence of how the medication works.”
The sections below cover each side effect individually with specific, actionable management strategies.
GLP-1 and Constipation
Constipation is the most common GLP-1 side effect — and the most predictable. When your gut slows down, bowel movements slow down too. The same mechanism driving your weight loss is behind this.
How to Manage It
- Exercise — even a short walk stimulates gut motility. After bariatric surgery, the first thing Dr. Yi tells patients to do is get up and move. The same principle applies on GLP-1s. Any physical movement helps get your bowels active.
- Eat smaller, more frequent meals. Three large meals create a backlog in a slowed gut. Breaking them into smaller portions throughout the day is easier for your digestive system to push through.
- Stay hydrated — aim for 64 ounces of water per day. Dehydration significantly worsens constipation and is easy to overlook when your appetite is suppressed. • Avoid processed foods, refined sugars, and high-fructose corn syrup. These compact into dense, hard-to-move masses in a slowed gut.
- Get 35 grams of fiber per day. A daily fiber supplement (like Metamucil) is something Dr. Yi takes personally and recommends even for people not on GLP-1s. For food sources, focus on beans, legumes, broccoli, spinach, and fruits with the skin on.
GLP-1 and Nausea
Nausea affects roughly 44 to 50 percent of people starting GLP-1 medications — making it the most discussed side effect. The cause is the same as constipation: delayed gastric emptying. Food sits in your stomach longer than it used to, and that causes nausea.
The good news: it almost always improves. For most patients, nausea decreases significantly by week five. It may return temporarily when your dose increases, but it settles again.
How to Manage It
- Eat smaller, more frequent meals throughout the day instead of three large ones • Move your body — a short walk stimulates the GI tract and helps ease nausea
- Try ginger and peppermint. Ginger tea, peppermint tea, ginger-flavored water, and peppermint gum all genuinely help. Dr. Yi prescribes peppermint gum for nausea in hospital patients routinely.
- Stop eating when you start burping. Burping is your body’s signal that your stomach is full. Put down the fork and give it time to catch up — continuing to eat past that point is what causes nausea to spike.
- Avoid carbonated beverages. Carbonation builds gas in a slowed stomach and makes nausea worse.
GLP-1 and Hair Loss: Why It Happens and How to Reverse It
Hair loss is one of the most alarming GLP-1 side effects 101 — but the cause is nutritional, not the medication itself. Hair loss on GLP-1s happens because you’re eating significantly less, and if you’re not deliberate about protein intake, your body falls short. When protein drops, hair loss follows. This is true for anyone losing weight rapidly, not just people on GLP-1 medications.
The other important thing to know: it is reversible.
How to Manage It
- Eat smaller, more frequent meals throughout the day instead of three large ones • Move your body — a short walk stimulates the GI tract and helps ease nausea
- Try ginger and peppermint. Ginger tea, peppermint tea, ginger-flavored water, and peppermint gum all genuinely help. Dr. Yi prescribes peppermint gum for nausea in hospital patients routinely.
- Stop eating when you start burping. Burping is your body’s signal that your stomach is full. Put down the fork and give it time to catch up — continuing to eat past that point is what causes nausea to spike.
- Avoid carbonated beverages. Carbonation builds gas in a slowed stomach and makes nausea worse.
GLP-1 and Heartburn: Managing Acid Reflux on GLP-1 Therapy
Heartburn affects about 10 percent of GLP-1 users. When food sits in a slowed stomach longer than usual, acid and small amounts of undigested food can reflux back up into the esophagus. If you already had heartburn before starting GLP-1 therapy, expect it to worsen.
How to Manage It
- Don’t eat within three hours of bedtime. There is a valve between your stomach and small intestine — once food passes through, it can’t back up. Giving yourself that buffer before lying down ensures your stomach is mostly emptied.
- Avoid trigger foods: red sauce, spicy food, citrus fruits, alcohol, and caffeine.
- Eat smaller, more frequent meals. Large meals increase pressure in the stomach.
- Over-the-counter medications that help: omeprazole (Prilosec), pantoprazole (Protonix), famotidine (Pepcid), and Tums. Some require a prescription; ask your provider.
GLP-1 Fatigue: Why You’re Tired and What to Do About It
Fatigue on GLP-1s is common, especially early in treatment. Your body is adjusting to a significant reduction in calorie intake — your system has been running on more fuel, and it takes time to recalibrate. Many patients also find the day after their injection is particularly rough, with exhaustion and nausea peaking in that 24-hour window.
How to Manage It
- Hydrate first. Dehydration is the most common and overlooked cause of fatigue. When your appetite is suppressed, thirst signals often disappear too. Drink water consistently throughout the day — 64 ounces minimum.
- Avoid caffeine and sugary drinks for an energy boost. They give a short spike and then a crash, plus they dehydrate you. The temporary lift isn’t worth the energy dip that follows.
- Exercise — even light activity improves energy and mental clarity. Movement is counterintuitive when you’re tired, but it genuinely works.
- Check your iron and B12. When protein and red meat intake drops, iron and B12 are often the first deficiencies to develop. A daily multivitamin covers both. If fatigue persists, ask your provider to run a blood panel.
- On injection days specifically: focus on protein water. If eating feels like too much, protein water is easier to get down than food and will prevent the energy crash from low protein.
One thing that often gets overlooked: some patients pull back from social situations when they start GLP-1 therapy — feeling shame about being on the medication, or wanting to avoid food-centered environments. That isolation worsens fatigue and low mood. Getting out and staying social, even for short walks or non-food activities, makes a meaningful difference.
Food Noise on GLP-1s: What It Is and How to Quiet It
Food noise is the persistent mental preoccupation with eating — constant thoughts about food, what you’re going to eat next, the snacks you used to have. It’s common in the early weeks of GLP-1 therapy when the medication is still titrating up and your established eating habits are being disrupted.
The important thing to know: for most patients, GLP-1s eventually reduce food noise significantly. The mental quiet around food is one of the most commonly reported benefits. But until the medication reaches therapeutic levels and new habits form, food noise can spike — especially when you’re bored or in environments associated with eating.
How to Manage It
- Stay mentally occupied. Boredom is the primary trigger. Sitting around watching TV is the worst-case scenario — your mind gravitates to food when there’s nothing else demanding attention.
- Choose activities that require active thinking — board games, card games, competitive sports, anything with a goal or score. These occupy the same mental bandwidth that food thoughts use.
- Meet friends in non-food settings. Go for a walk, do something active. Avoid sitting around food-centered environments in early weeks if food noise is strong.
- Exercise. Physical activity is the most effective tool for redirecting mental energy. Something competitive — tennis, pickleball, rock climbing — works especially well because it demands full attention and has a clear goal.
Why You Feel Cold on GLP-1s
Feeling unusually cold — even indoors, even in mild weather — is a recognized and common GLP-1 side effect that most patients don’t expect.
The cause is metabolic. When your caloric intake drops significantly, your metabolism slows down to adjust to the reduced fuel level. Lower metabolism produces less heat, and you feel cold. This is your body doing exactly what it’s supposed to do — not a sign anything is wrong.
This is temporary. Your metabolism recalibrates as your body adjusts to the new intake level. In the meantime, it’s actually a signal that the medication is working.
Supplements to Discuss With Your Provider
Because GLP-1 medications reduce how much you eat, nutritional gaps are a real risk. These are the supplements Dr. Yi recommends reviewing with your provider — not everyone needs all of them, and the right amounts depend on your individual health profile.
| Supplement | Why It Matters on GLP-1s | Notes from Dr. Yi |
| Daily multivitamin | Covers broad nutritional gaps from reduced food intake | Dr. Yi takes a prenatal vitamin daily — complete coverage in one dose |
| Protein (food-first, then supplement) | Prevents muscle loss and hair loss | Target 0.8–1.1g per kg body weight; protein water is an easy option when food is hard to eat |
| Fiber (35g/day) | Prevents constipation from slowed gut motility | Metamucil or equivalent; also from beans, legumes, and fruit with skin |
| B12 | Drops when animal protein intake decreases | Found in most multivitamins; check levels if fatigue persists |
| Vitamin D | Widely deficient in the general population regardless of GLP-1 use | Most people need supplementation; hard to overdose on standard doses |
| Biotin + Selenium | Supports hair health during periods of rapid weight loss | Found in most multivitamins; can also supplement separately |
Source: National Library of Medicine — Nutritional Considerations During Weight Loss Therapy
The Day After Your Injection: What to Expect
Many patients find the day after their weekly injection is consistently the toughest day — exhaustion, nausea, and feeling generally off. This is very common and not a reason to stop.
Dr. Yi’s specific advice for injection day recovery:
- Make hydration your priority above everything else. If eating feels like too much, don’t force it.
- Drink protein water throughout the day. It’s lighter than food or protein shakes, easier on a sensitive stomach, and prevents the energy crash from low protein and low hydration simultaneously.
- Skip caffeine and sugar — they’ll worsen the crash that follows.
- This pattern typically improves after the first several weeks as your body adjusts to the medication cycle.
Do You Have to Take GLP-1 Medications Forever?
No — and Dr. Yi is direct about this. Medication companies have an interest in long-term prescribing, but the clinical goal is different.
GLP-1 medications work best as a catalyst. The job isn’t to stay on them indefinitely — it’s to use the window of reduced appetite and reduced food noise to build sustainable dietary habits and an exercise routine that your body can maintain on its own.
Here is the key insight: exercise itself naturally raises GLP-1 levels in your body. People who are already fit and maintain their weight easily do so in part because their bodies are producing GLP-1 naturally through regular movement and established habits. They’re already in that metabolic sweet spot.
That’s the goal. Use the medication to get into a healthy routine, build the habits, and eventually your body will support that lifestyle without needing the medication. Once you’re there — eating well, moving regularly, in a sustainable calorie balance — many patients are able to taper off and maintain their results.
The side effects, the difficult first weeks, the adjustment period — they’re all part of building toward that place.
Frequently Asked Questions
The most common GLP-1 side effects are constipation, nausea, diarrhea, and heartburn. All four come from the same cause: the medication slows down your digestive system, which is also how it drives weight loss. Most side effects improve within the first few weeks. Nausea typically resolves by week five. Constipation responds well to hydration, fiber, and regular exercise.
To manage GLP-1 nausea, eat smaller and more frequent meals, stay hydrated, and try ginger or peppermint in tea, water, or gum form. Stop eating when you start burping — that’s your body signaling the stomach is full. Avoid carbonated drinks. If nausea is severe, ask your provider about Zofran (ondansetron), a prescription anti-nausea medication with a low side effect profile used routinely for post-surgical nausea.
Hair loss can occur on GLP-1 therapy, but it is caused by inadequate protein intake — not the medication itself. When you eat significantly less, protein often drops below what’s needed to sustain hair growth. The fix is nutritional: eat protein first at every meal, use protein shakes or protein water if solid food is difficult, and take a daily multivitamin with biotin and selenium. GLP-1 related hair loss is reversible once protein intake is adequate.
GLP-1 medications slow different sections of the digestive system at different rates. When the stomach, small intestine, and colon are moving at different speeds, the timing of digestion gets disrupted — which can cause constipation in some phases and diarrhea in others, sometimes alternating. Staying hydrated, eating small frequent meals, and avoiding alcohol and sugar helps manage both.
GLP-1 fatigue is usually caused by reduced calorie intake combined with dehydration. To manage it: drink at least 64 ounces of water per day, avoid caffeine and sugary drinks for energy (they cause a crash), take a daily multivitamin with B12 and iron, and incorporate light exercise. On injection days, protein water throughout the day helps prevent the energy crash that comes from both low hydration and low protein.
Food noise is the persistent mental preoccupation with eating — constant thoughts about food, cravings, and what to eat next. It’s common early in GLP-1 therapy while habits are adjusting. For most patients, food noise decreases significantly as the medication reaches therapeutic levels. Staying mentally occupied with goal-oriented activities — competitive games, exercise, socializing — helps manage it in the meantime.
Yes. Feeling unusually cold is a recognized GLP-1 side effect. When caloric intake drops significantly, metabolism slows to match the reduced fuel level. Lower metabolism produces less body heat. This is temporary and improves as your body adjusts to the new intake level.
No. The clinical goal is to use GLP-1 therapy as a catalyst to build sustainable dietary and exercise habits. Exercise naturally raises GLP-1 levels in your body — people who are already fit maintain their weight partly because of naturally elevated GLP-1 from regular movement. Once those habits are established, many patients taper off the medication and maintain their results without it.
No — this is a common misconception. Eating less frequently actually produces larger insulin spikes. Smaller, more frequent meals throughout the day keep insulin levels more stable. Dr. Yi specifically recommends moving away from three large meals per day when on GLP-1 medications.
There is no strong head-to-head data showing meaningfully different side effect profiles between the two. Tirzepatide produces higher average weight loss — around 22.5% of body weight versus 17.4% for semaglutide — which means similar results may be achievable at a lower dose, potentially with fewer side effects. But this is clinical reasoning rather than proven data.
Related Resources
For a complete overview of how GLP-1 medications work, realistic weight loss expectations, candidacy, and nutrition guidance from a surgeon and registered dietitian: [LINK]
To watch the full Understanding GLP-1s webinar with Dr. Yi and registered dietitian Kristen Kirkpatrick.
Ready to start your GLP-1 journey with medical supervision and expert support: → Get Started with OrderlyMeds
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. It is based on a recorded webinar with a board-certified general and bariatric surgeon. GLP-1 medications require a prescription and a clinical evaluation. Individual results and side effect experiences vary. Always consult a qualified healthcare provider before starting, adjusting, or stopping any medication or supplement regimen.
