Side Effects
Understanding Side Effects of GLP-1 Medications
GLP-1 medications work by changing how your stomach empties and how your body handles food, which is why side effects can happen. Everyone’s experience is different, some people feel very little, while others need time to adjust. Knowing what to expect and how to manage it helps you stay on treatment and get the most benefit.
Common Side Effects
Around 40–70% of people experience side effects while taking GLP-1 medications. The good news is that, with the right strategies, most side effects are mild, manageable, and often fade after the first few weeks.
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Why it happens: Nausea is the most common side effect of GLP-1s, especially when first starting or after a dose increase. It happens because:
The medication slows stomach emptying, so food sits longer and triggers queasiness.
Dose changes temporarily shock your system as your gut adjusts.
Dehydration, greasy or heavy meals, or overeating can make it worse.
In rare cases, vomiting may be linked to more serious issues like severe dehydration or gallbladder problems.
What can help:
Start low, go slow: ask your provider about gradual dose increases.
Eat smaller, more frequent meals instead of large portions.
Avoid greasy, fried, or spicy foods that are harder to digest.
Stay hydrated: sip water or electrolyte drinks throughout the day.
Soothing options: ginger, peppermint tea, or bland foods like crackers or rice.
If symptoms persist: your provider may recommend anti-nausea medication (like Zofran®).
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Why it happens: About 5–25% of people on GLP-1s experience diarrhea, most often in the first few weeks. It happens because:
The medication changes how food and fluids move through the gut, speeding things up.
Dose changes can temporarily irritate the digestive system.
Certain foods (especially greasy or fatty) can make symptoms worse.
In some cases, medication combinations (like GLP-1s + metformin) increase the risk.
What can help:
Avoid fatty or greasy foods that make diarrhea worse.
Eat soluble fiber (oats, bananas, applesauce, rice) to bulk up stools.
Stay hydrated with water or electrolyte drinks to replace lost fluids.
Consider probiotics (yogurt, kefir, or supplements) to restore gut balance.
OTC support: bismuth subsalicylate (Pepto-Bismol®) or loperamide (Imodium®) can help short-term if approved by your provider.
Ask about interactions: your provider may adjust other meds, like lowering metformin if diarrhea persists.
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Why it happens: Constipation is one of the most common GLP-1 side effects and can persist throughout treatment. It happens because:
GLP-1s slow digestion, so food moves through the gut more slowly.
Dehydration makes stools harder and more difficult to pass.
Low fiber intake or not enough activity can worsen symptoms.
In very rare cases, severe constipation may lead to hardened stomach masses (bezoars).
What can help:
Hydrate well: aim for clear to light-yellow urine.
Eat more fiber: fruits, vegetables, beans, lentils, whole grains.
Stay active: even walking helps stimulate the bowels.
Fiber supplements: Metamucil (psyllium), Benefiber (wheat dextrin), Citrucel (methylcellulose).
Laxatives if needed: Miralax (polyethylene glycol) or magnesium citrate, with provider guidance.
Stool softeners: Colace (docusate sodium) can make stools easier to pass.
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Why it happens: Reflux and sulfur burps are common side effects of GLP-1s. These medications slow how quickly food leaves the stomach, which increases the chance of heartburn, sour taste, and bloating. Food that lingers can also ferment, producing hydrogen sulfide gas — the “rotten egg” smell of sulfur burps. This effect is uncomfortable but usually temporary.
What can help:
Eat smaller, more frequent meals.
Stay upright for at least 2 hours after eating.
Limit trigger foods: greasy, spicy, sulfur-rich (eggs, broccoli, cabbage, garlic), and carbonated drinks.
Chew slowly and avoid swallowing excess air.
Stay hydrated and move daily to support digestion.
Over-the-counter relief: Tums, Pepcid (famotidine), or Prilosec (omeprazole) for reflux; simethicone (Gas-X, Phazyme) or Pepto-Bismol for gas and sulfur burps.
Talk with your provider if symptoms persist, worsen, or are paired with vomiting or severe stomach pain.
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Why it happens: GLP-1s slow digestion, which can make food sit in the stomach longer. This pressure may cause aching, fullness, or cramping. Eating large or greasy meals can make symptoms worse. In some cases, pain may also come from constipation or gas. Rarely, stomach pain can signal gallbladder problems or pancreatitis.
What can help:
Eat smaller meals and avoid overeating.
Limit greasy or fried foods that are harder to digest.
Gentle walking or light activity can ease pressure.
A heating pad on the abdomen may help mild cramps.
Call your doctor if the pain is sharp, severe, radiates to your back, or does not go away.
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Why it happens: Mild redness, itching, swelling, or small bumps at the injection site are common with GLP-1s. These usually improve within a few hours to days. Rarely, hives or more severe reactions can occur.
What can help:
Rotate injection sites between the stomach, thigh, and upper arm.
For the stomach: use the left side, right side, or middle area, but always inject at least 2 inches away from the belly button.
Let the medication warm to room temperature before injecting.
Use proper injection technique and clean with alcohol wipes.
Apply a cool compress if redness or itching develops.
Call your provider if reactions are severe, spreading, or do not improve.
Secondary Side Effects
These are not caused directly by GLP-1s but often happen because of common side effects like nausea, vomiting, diarrhea, or rapid weight loss.
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Why it happens: Dehydration can occur if nausea, vomiting, or diarrhea cause too much fluid loss. It is most common in the first few weeks of treatment or after dose increases. Dehydration can also make other side effects worse, such as dizziness, headaches, and constipation.
What can help:
Drink water consistently throughout the day instead of large amounts all at once.
Use electrolyte drinks if you have vomiting, diarrhea, or are sweating.
Check urine color — aim for light yellow to clear.
Avoid greasy or spicy foods that worsen nausea and fluid loss.
Raise your dose slowly to reduce GI side effects that trigger dehydration.
Call your doctor if you notice dark urine, dizziness, a fast heartbeat, or if you are urinating very little.
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Why it happens: Some people on GLP-1s feel unusually tired, flat, or unmotivated. This can happen when first starting or after dose increases. Possible reasons include lower calorie intake, changes in dopamine pathways that affect energy and pleasure, and dehydration or poor nutrition. For some, it shows up as simple fatigue, while others describe it as “the blahs” or a loss of interest in things they usually enjoy.
What can help:
Talk to your provider about lowering or slowing the dose.
Make sure you are eating enough protein, calories, and balanced meals.
Stay lightly active — walking, stretching, or resistance exercise can boost both mood and energy.
Prioritize sleep and hydration.
If low mood persists, your provider may suggest medications such as Wellbutrin (bupropion) or other mental health support.
Reach out quickly if you notice persistent sadness, numbness, or loss of interest in life.
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Why it happens: Hair changes are not a direct effect of GLP-1s, but some people notice temporary shedding during rapid weight loss. This is called telogen effluvium and happens when the body shifts energy away from hair growth. Poor nutrition, low protein intake, or stress can also contribute. Rarely, GLP-1s may play a role in hair loss, but evidence is limited.
What can help:
Eat enough protein, iron, zinc, and vitamins to support hair health.
Aim for steady, gradual weight loss rather than very rapid changes.
Manage stress and get good sleep, both of which support healthy hair cycles.
Over-the-counter supplements like biotin or collagen may help, though results vary.
Hair shedding often improves within 3–6 months as weight and nutrition stabilize.
Talk to your provider if shedding is severe or does not improve.
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Why it happens: Some lean mass loss is normal during weight loss, including muscle. GLP-1s can also reduce appetite, which sometimes leads to eating too little protein or calories. This may cause weakness or fatigue. Cramps are usually linked to dehydration or low electrolytes from nausea, vomiting, or diarrhea.
What can help:
Do resistance exercise such as light weights, resistance bands, or bodyweight training to maintain muscle.
Eat enough protein and calories to support muscle and energy needs.
Stay hydrated and consider electrolyte drinks if you are sweating or sick.
Stretch regularly to prevent cramps and improve circulation.
Call your doctor if cramps are severe, persistent, or if weakness interferes with daily activities.
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Why it happens: GLP-1s alone rarely cause low blood sugar. The risk goes up if they are used together with insulin or sulfonylureas (like glipizide or glyburide). Skipping meals, undereating, or drinking alcohol can also trigger hypoglycemia.
What can help:
Eat regular meals and snacks with protein and fiber to keep blood sugar stable.
Carry quick carbs like glucose tablets, juice, or regular soda to treat sudden lows.
Monitor blood sugar more often if you are on insulin or sulfonylureas.
Talk to your provider about adjusting medications if low blood sugar happens frequently.
Call your doctor right away if you have repeated lows, fainting, seizures, or confusion.
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Why it happens: GLP-1s themselves do not usually lower blood pressure directly, but they can contribute if you are losing weight quickly, eating less, getting dehydrated from nausea, vomiting, or diarrhea, or already taking blood pressure medication. This can lead to lightheadedness, dizziness, or fainting, especially when standing up.
What can help:
Stay hydrated with water and electrolyte drinks if you are sick or sweating.
Eat balanced meals to help maintain steady blood pressure.
Stand up slowly from sitting or lying down to prevent sudden drops.
Track your blood pressure at home if you are on BP medications.
Call your doctor if blood pressure readings are consistently low, if you faint, or if you have chest pain or confusion. Your medications may need adjustment.
Rare Serious Side Effects
Most people will never experience these side effects but if you do notice severe abdominal pain, persistent vomiting, swelling, trouble swallowing, or sudden vision changes, contact your doctor right away.
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Why it happens: In rare cases, gallstones or other issues can block the pancreatic duct, leading to painful inflammation of the pancreas. GLP-1s themselves have not been proven to directly cause pancreatitis, but the risk exists.
What can help:
Be alert for severe, persistent stomach pain that radiates to your back, often with nausea or vomiting.
Seek medical care immediately if these symptoms appear.
Your provider may run tests and stop the medication if pancreatitis is suspected.
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Why it happens: GLP-1s don’t usually harm the kidneys directly. Problems can occur if dehydration from nausea, vomiting, or diarrhea reduces blood flow to the kidneys. Rarely, kidney inflammation (interstitial nephritis) has been reported.
What can help:
Stay hydrated, especially if you are sick or have GI side effects.
Be cautious with medications that strain the kidneys (NSAIDs, ACE inhibitors, ARBs).
Call your doctor if you notice swelling, confusion, dark urine, or urinating very little.
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Why it happens: Rapid weight loss can increase the chance of gallstones forming, which may block bile flow and cause gallbladder attacks. GLP-1s have been linked to a slightly higher risk of gallbladder disease, especially in the first 6 months of treatment.
What can help:
Aim for gradual weight loss instead of losing weight too quickly.
Watch for upper right abdominal pain, nausea, or pain after fatty meals.
Call your doctor right away if symptoms occur — untreated gallstones can lead to infection or pancreatitis.
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Why it happens: Rapid improvements in blood sugar from GLP-1s can temporarily worsen existing diabetic retinopathy. Blurred vision or floaters are sometimes reported early in treatment.
What can help:
Schedule regular eye exams, especially if you already have diabetic eye disease.
Aim for steady, gradual improvements in blood sugar to reduce risk.
Report new vision changes — blurred vision, floaters, or sudden vision loss — to your doctor right away.
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Why it happens: In rodent studies, GLP-1s caused thyroid C-cell tumors. This risk has not been shown in humans, but people with a family history of medullary thyroid cancer (MTC) or MEN2 should avoid these drugs.
What can help:
Report any new neck lumps, hoarseness, or trouble swallowing to your doctor.
If you have a family history of thyroid cancer, genetic testing may be recommended.
Remember: thyroid cancer is very rare, and most people are not at increased risk.
