GLP-1 Weight-Loss Drugs: How They Work, Options, Side Effects

GLP-1 Weight-Loss Drugs: How They Work, Options, Side Effects

GLP-1 weight-loss drugs, such as semaglutide and the dual-action tirzepatide, copy a gut hormone that reduces appetite, slows stomach emptying and helps control blood sugar. In large trials they led to average weight loss of roughly 15% to 18% of body weight over about 16 to 18 months, alongside diet and activity changes. Nausea and other stomach side effects are common.

This guide is for adults who are considering a GLP-1 medicine, or already taking one, and want a clear, neutral explanation before talking with their doctor. We use generic drug names only.

Key takeaways

  • GLP-1 receptor agonists are approved for weight management in adults with a BMI of 30 or more, or 27 or more with a weight-related condition such as high blood pressure or type 2 diabetes.
  • In the 68-week STEP 1 trial, weekly semaglutide 2.4 mg led to an average 14.9% weight loss, compared with 2.4% on placebo.
  • In the FDA's review of tirzepatide, adults without diabetes on the 15 mg dose lost an average of 18% of body weight compared with placebo over 72 weeks.
  • Nausea affected 44.2% of semaglutide users in STEP 1, and the drugs should not be used with a personal or family history of medullary thyroid cancer or MEN 2.
  • Facial hollowing after treatment comes from rapid fat loss, not from the drug itself, and losing weight more slowly can reduce it.

What is GLP-1 and how do GLP-1 drugs work?

GLP-1 (glucagon-like peptide-1) is a hormone your small intestine releases after you eat. GLP-1 receptor agonists are medicines that mimic it, binding to the same receptors to lower blood sugar and reduce appetite.

According to Cleveland Clinic, these drugs work in four main ways:

  • More insulin when you need it. They prompt the pancreas to release insulin after meals.
  • Less glucagon. They block glucagon, a hormone that pushes stored sugar into the bloodstream.
  • Slower stomach emptying. Food leaves the stomach more slowly, which blunts blood sugar spikes and helps you feel full longer.
  • Appetite signals in the brain. They act on brain areas that control hunger and fullness, so you tend to eat less.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that liraglutide and semaglutide mimic GLP-1, while tirzepatide mimics both GLP-1 and a second gut hormone, GIP (glucose-dependent insulinotropic polypeptide). That dual action is why tirzepatide is sometimes called a "dual agonist."

The first drug in this class, exenatide, was approved in 2005 for type 2 diabetes. If you're unclear on how the two main types of diabetes differ, our explainer on type 1 vs type 2 diabetes is a useful primer.

Which weight-loss medicines are available, and how do they compare?

In the US, seven medicines are FDA-approved for long-term weight management; three of them act on GLP-1. Older, non-GLP-1 drugs remain useful for some people.

The table lists the long-term options named by NIDDK, with dosing details from Cleveland Clinic and the FDA.

Medicine (generic)TypeHow it's takenNotes
SemaglutideGLP-1 receptor agonistInjection once weekly (a daily tablet exists for diabetes)14.9% average loss in STEP 1
TirzepatideGLP-1 and GIP agonistInjection once weekly, dose raised over 4 to 20 weeks18% average loss vs placebo at 15 mg
LiraglutideGLP-1 receptor agonistInjection once dailyOlder GLP-1 option
Phentermine-topiramateAppetite suppressant plus anti-seizure drugCapsule dailyNon-GLP-1 option
Naltrexone-bupropionActs on brain reward and appetite pathwaysTablets dailyNon-GLP-1 option
OrlistatBlocks fat absorption in the gutCapsule with mealsLower dose sold without prescription
SetmelanotideTargets a specific appetite pathwayInjectionOnly for certain rare genetic disorders

Phentermine on its own is approved only for a few weeks of use. NIDDK reports that, on average, adults taking a weight-loss medicine plus a lifestyle program lose 3% to 12% more of their starting weight after a year than those making lifestyle changes alone, and most of the loss happens in the first 6 months.

How much weight do people lose on GLP-1 drugs?

Results in trials are larger than with older drugs. In the STEP 1 trial of 1,961 adults, summarized by the American College of Gastroenterology, weekly semaglutide 2.4 mg produced an average 14.9% weight loss over 68 weeks, compared with 2.4% on placebo. About half (50.5%) of people on semaglutide lost at least 15% of their body weight.

For tirzepatide, the FDA's approval announcement reports that adults without diabetes on the 15 mg dose lost an average of 18% of body weight compared with placebo over 72 weeks; in adults with type 2 diabetes the figure was 12%. Trial results are averages. Some people lose much more and some much less.

Who are GLP-1 weight-loss drugs for?

They're for adults with obesity or with overweight plus a weight-related health problem, used together with a reduced-calorie diet and more physical activity. They are not cosmetic drugs for modest weight loss.

According to NIDDK, you may qualify if you have:

  • A BMI of 30 or more, or
  • A BMI of 27 or more and a weight-related condition such as high blood pressure or type 2 diabetes.

Some medicines are also approved for children aged 12 and older. NIDDK notes that if you haven't lost at least 5% of your starting weight after 12 weeks on the full dose, your clinician will probably suggest stopping. People who respond well and have no serious side effects may stay on treatment long term, because most people regain some weight when they stop.

Diet still matters. Eating less on these drugs makes protein intake and food quality more important, not less. Our guides to how much protein you need per day and foods that support fullness the way GLP-1 does cover the food side.

What are the side effects of GLP-1 drugs?

The most common side effects are stomach-related: nausea, diarrhea, vomiting and constipation, usually worst when starting or raising the dose. Serious problems are rare but include pancreatitis and gallbladder disease.

In STEP 1, nausea affected 44.2% of people on semaglutide (vs 17.4% on placebo) and diarrhea 31.5% (vs 15.9%). Only 4.5% stopped the drug because of stomach side effects.

Common side effectsRare but serious risks
Nausea, vomiting, diarrhea, constipationPancreatitis (inflammation of the pancreas)
Abdominal discomfort, burping, refluxGallbladder problems
Reduced appetite, indigestionLow blood sugar, especially with insulin or sulfonylureas
Fatigue, headache, dizzinessAcute kidney injury
Injection site redness or itchingWorsening diabetic eye disease (retinopathy)
Hair loss (reported with tirzepatide)Severe allergic reactions

This list draws on Cleveland Clinic and the FDA. Thyroid C-cell tumors were seen in rats; it isn't known whether this happens in humans, but people with a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2 (MEN 2) should not use liraglutide, semaglutide or tirzepatide. The FDA also lists suicidal thoughts or behavior among the warnings it is monitoring, and NIDDK notes the agency is still studying whether the drugs cause this.

These drugs should not be used during pregnancy or when planning a pregnancy, and NIDDK says they're not recommended while breastfeeding. Tirzepatide hasn't been studied in people with severe gastroparesis, a condition where the stomach empties very slowly; our article on eating with gastroparesis explains why slowed emptying matters.

Why does your face change on GLP-1 drugs?

Facial hollowing on these drugs is caused by rapid weight loss, not by the medicine itself. Losing fat under the skin quickly can leave the face looking gaunt or older.

Cleveland Clinic describes the changes as sunken cheeks and eyes, new wrinkles, thinner lips, jowls and loose skin on the face and neck. Fat loss under the skin causes hollowing, and lower collagen and elastin reduce the skin's ability to snap back. The same thing can happen after bariatric surgery or any very fast weight loss. Older adults are more affected because they have less facial fat to begin with.

The changes don't harm your health and don't go away on their own if you keep the weight off. To reduce them, Cleveland Clinic suggests:

  1. Aim for slower loss, about 1 to 2 pounds a week, by talking to your doctor about dose pacing.
  2. Eat enough protein to protect muscle while you lose fat.
  3. Stay hydrated.
  4. Use a consistent skin care routine and daily sunscreen.
  5. Combine the medicine with regular exercise, including strength training.

If loose skin bothers you, options range from microneedling and radiofrequency tightening to fillers and surgery. Our articles on loose neck skin after weight loss and a simple strength training plan cover practical next steps.

Common mistakes with GLP-1 treatment

  • Skipping meals and protein. Low appetite can lead to very low intake, which speeds muscle loss. Plan small, protein-rich meals. Our article on losing muscle mass explains the warning signs.
  • Rushing dose increases. Doses are raised gradually to limit nausea. Moving faster than prescribed often backfires.
  • Getting dehydrated. Vomiting or diarrhea plus low fluid intake raises the risk of kidney problems.
  • Combining GLP-1 drugs. The FDA says tirzepatide should not be used with another GLP-1 receptor agonist.
  • Treating the drug as the whole plan. Approval is for use with diet and activity changes, and most people regain some weight after stopping.

When to see a doctor

Contact your doctor, or get emergency care where noted, if you're taking a GLP-1 drug and have:

  • Severe, persistent abdominal pain, with or without vomiting, which can signal pancreatitis or gallbladder disease.
  • Vomiting or diarrhea that stops you keeping fluids down, or very little urine.
  • A lump or swelling in the neck, hoarseness, trouble swallowing or shortness of breath.
  • Shaking, sweating, confusion or a fast heartbeat, especially if you also take insulin or a sulfonylurea (possible low blood sugar).
  • Changes in vision if you have diabetes.
  • New or worsening depression, or thoughts of harming yourself. If you're in immediate danger, call emergency services.
  • Hives, facial swelling or trouble breathing after an injection, which is an emergency.
  • A pregnancy, or plans to become pregnant.

FAQ

How long does it take for GLP-1 drugs to work?

Appetite often drops within the first weeks, but doses are increased gradually, so weight loss builds over months. NIDDK notes most loss from weight medicines happens in the first 6 months. If you haven't lost at least 5% of your starting weight after 12 weeks on the full dose, your clinician may suggest stopping.

What happens when you stop a GLP-1 drug?

Appetite usually returns and most people regain some weight, according to NIDDK. That's why these medicines are often used long term in people who respond well and tolerate them. If you plan to stop, talk to your doctor first about tapering and a plan to protect the habits you've built.

Is semaglutide or tirzepatide better for weight loss?

In separate trials, tirzepatide produced slightly larger average losses than semaglutide, but side effects, cost, coverage and your health conditions all matter. The trials weren't identical, so direct comparisons are imperfect. Your doctor can weigh these factors, including any heart, kidney or diabetes needs.

Can you prevent facial changes on GLP-1 drugs?

You can reduce them. Cleveland Clinic links the changes to how fast you lose weight, so slower loss of about 1 to 2 pounds a week helps, along with enough protein, good hydration, sunscreen and strength training. Older adults are more prone because they start with less facial fat.

What to do next

  1. Work out your BMI and list any weight-related conditions before your appointment.
  2. Ask your doctor about all options, including non-GLP-1 medicines, and about cost and coverage.
  3. If you start treatment, plan protein-rich meals and two or more strength sessions a week from day one.
  4. Keep a short log of side effects, weight and appetite to review at each dose change.

This article is for general information and is not medical advice. Only a clinician who knows your medical history can decide whether a GLP-1 medicine is right for you.

Sources

Last reviewed: October 2026.

Comments

Post a Comment

Popular Posts

Top 10 Exercises to Help You Sleep Longer and Better

Image
The best exercises for sleep are the ones you'll do most days: brisk walking, yoga, swimming, cycling, strength training and gentle evening stretching all have research linking them to falling asleep faster and sleeping more deeply. Moderate activity can fit almost any time of day. Hard, sweaty workouts are usually best kept away from the last couple of hours before bed. This guide is for you if you lie awake at night, wake up unrefreshed, or want a drug-free way to sleep better, and you'd like to know which kind of movement to try first. Key takeaways Regular activity over weeks matters more than any single workout. Expect gradual change, not an overnight fix. Morning walks outdoors pair movement with daylight, which helps set your body clock. Slow, breath-focused practices such as yoga, tai chi and stretching are the best fit for evenings. Save high-intensity workouts for morning or early afternoon if late sessions keep you up. Exercise helps most sleep problems but...
Read more

Muscle Gain Diet: What Actually Works, Kept Simple

Image
To build muscle, most people who lift regularly need about 1.4 to 2.0 grams of protein per kilogram of body weight a day, spread over meals of roughly 20 to 40 grams each, plus enough total food to fuel training. Add consistent strength training and decent sleep, and that covers most of the results. Everything else is fine-tuning. This guide is for anyone who has started lifting and feels buried in conflicting advice about meal timing, shakes and supplement stacks. Here's the short, evidence-based version. Key takeaways The International Society of Sports Nutrition (ISSN) says 1.4 to 2.0 g of protein per kg per day is enough for most exercising people building muscle. Spread protein across the day, about 20 to 40 g per meal, every 3 to 4 hours. Exact timing around your workout matters less than total daily intake. Eating before or after training both work. Creatine monohydrate is the best-supported supplement. Protein powder is a convenience, not a requirement. If you...
Read more

Why Am I Losing Muscle Mass? Causes, Signs and Fixes

Image
Most unexplained muscle loss comes from using your muscles less, getting older, or eating too little protein and energy. Less often, it's a sign of nerve damage, a hormone problem or another illness. The good news is that the common causes respond well to regular strength training and enough protein at each meal. Maybe your legs look thinner after a few months at a desk job, or the stairs feel harder than they did last year. This guide is for anyone who has noticed that change and wants to know what's behind it and what to do next. Key takeaways Disuse is the most common cause: muscles shrink when they aren't worked regularly, and this type can often be reversed with exercise and better nutrition. Age plays a part: Cleveland Clinic says age-related muscle loss (sarcopenia) starts in your 30s or 40s and speeds up between ages 65 and 80. Strength training is the main fix: adults should do muscle-strengthening activity on at least 2 days a week, according to the CD...
Read more

Plant Protein Powder for Acne-Prone Skin: What to Know

Image
If your skin broke out after you started whey protein shakes, switching to a plant-based protein powder is a reasonable experiment. Cow's milk has been linked with acne, and case reports describe acne flares that cleared after whey was stopped. A pea protein powder can support muscle growth, and one trial found results similar to whey. This guide is for people who lift or train and want to keep building muscle without guessing about their skin. It covers what the evidence does and doesn't show, how to choose a powder and how to run a fair test. Key takeaways The milk link is real but not fully explained: the American Academy of Dermatology (AAD) says studies link cow's milk with acne, though the reason isn't clear. Whey evidence is limited: it comes mostly from small case reports and observational studies, not large trials. Pea protein can build muscle: in a 12-week trial, pea and whey produced similar gains in muscle thickness. Sugar matters too: high-gly...
Read more

Calorie Deficit and Insomnia: Why Dieting Keeps You Awake

Image
Yes, a calorie deficit can cause insomnia. Eating less than you burn lowers overnight blood sugar, raises the hunger hormone ghrelin and nudges cortisol up, and together those signals can wake you at 2 or 3 a.m. The bigger and faster the deficit, the more likely your sleep suffers. This guide is for anyone who started a diet and suddenly sleeps worse. You'll learn how to recognize diet-related sleep trouble, and how to adjust your plan so you keep losing fat without lying awake staring at the ceiling. Key takeaways Diet-related sleep trouble usually looks like waking in the second half of the night, not trouble falling asleep. Large, fast deficits disrupt sleep more than small, steady ones. Keeping protein adequate and saving some carbohydrate for the evening often helps. Poor sleep makes dieting harder: it raises hunger and can shift weight loss away from fat and toward muscle. Loud snoring, gasping, or insomnia that started before the diet needs a medical check, not a ...
Read more

Can Pinworms Last for Years? Why Infections Keep Coming Back

Image
No, a single pinworm can't live in your body for years. Adult worms live for only a few weeks. What makes an infection seem to last for months, or even years, is reinfection: eggs get swallowed again and start a new cycle before the old one ends. Break that cycle and the infection clears. This is for parents who've treated a child, seen the itching come back a few weeks later, and started to wonder whether something more serious is going on. Key takeaways Pinworms live for weeks, not years. Long-running "infections" are almost always repeated reinfections. Treatment is two doses of medicine, two weeks apart, because the medicine kills worms but not eggs. Everyone in the household needs treating at the same time, even people with no symptoms. Eggs can survive on bedding, clothes and surfaces for around two to three weeks, so cleaning matters as much as medicine. Pinworm rarely causes serious harm, but see a doctor for babies under 2, during pregnancy, or if t...
Read more

No-Sugar Diet: How to Cut Added Sugar Step by Step

Image
A no-sugar diet means cutting added sugars, not the natural sugar in whole fruit, vegetables and plain dairy. You drop soda, sweets and sweetened snacks first, then hunt down hidden sugar in sauces, bread, yogurt and cereal. Most people get through the hardest cravings within one to two weeks. It sounds simple until you start reading labels and find sugar in pasta sauce, salad dressing and "healthy" granola. This guide is for anyone who wants to cut back without a miserable, all-or-nothing approach that collapses by week two. Key takeaways The target is added and free sugars: table sugar, syrups, honey, fruit juice and sweeteners added to processed food. The WHO advises keeping free sugars under 10% of daily calories, with extra benefit below 5%, about 25 grams or 6 teaspoons a day. The CDC reports that US adults average about 17 teaspoons of added sugar a day. Expect cravings, irritability or low energy for the first few days; they usually ease within one to two we...
Read more

Fruits That Help Reduce Cholesterol and What to Avoid

Image
Avocado, berries, oranges and an apple, fruits that fit a cholesterol-friendly diet Fruits that are rich in soluble fiber, such as apples, pears, oranges, bananas and prunes, can help lower LDL ("bad") cholesterol as part of an overall heart-healthy diet. Avocado can help too when it replaces saturated fat. Fruit alone won't fix high cholesterol, but it's one of the easiest changes to stick with. This guide is for anyone who's just seen a high cholesterol result and wants to know what to put on the plate, and what to watch out for, especially if you take a statin. Key takeaways MedlinePlus lists apples, bananas, oranges, pears and prunes as fruit sources of soluble fiber, which helps lower cholesterol. The suggested target is 10 to 25 grams of soluble fiber a day, from fruit, oats, beans and other foods. In a small controlled study, a moderate-fat diet with one avocado a day lowered LDL more than a similar diet without avocado. Grapefruit, Seville ora...
Read more

Soursop Benefits and Risks: Fruit, Leaves and Tea

Image
Soursop fruit is a healthy, fibre-rich tropical fruit that's safe to enjoy in normal amounts. Its leaves and tea have traditional uses with some early lab and animal evidence, but no human trials show soursop treats or cures cancer. High-dose leaf extracts and supplements also raise real concerns about nerve damage, so they deserve caution. This is for anyone who enjoys soursop, has been told to drink the leaf tea for a health problem, or has seen posts claiming it beats chemotherapy and wants a straight answer. Key takeaways The fruit pulp offers fibre, vitamin C and potassium, and fits well in a varied diet. Soursop extracts kill some cancer cells in lab dishes, but that hasn't been shown in people. No reputable cancer organisation supports it as a treatment. Compounds in soursop, especially concentrated in leaves, seeds and bark, can harm nerve cells. Heavy long-term use has been linked to Parkinson-like symptoms. Occasional leaf tea is different from daily concentr...
Read more

Why Sleep Earbuds Cause a Sore Spot on Your Ear Cartilage

Image
A sore spot on your ear after sleeping with earbuds is a small pressure injury, not an infection. The outer ear has almost no fat padding, and its cartilage has no blood vessels of its own. When an earbud is trapped between your head and the pillow for hours, it squeezes the tiny vessels that feed that cartilage, and the tissue complains by morning. If you use audio to fall asleep, you probably know the pattern: the sound helps, but one ear wakes up tender, and the tenderness sits on the rim rather than deep in the canal. That pattern is predictable, and it's worth understanding before it turns into a lump that lingers for months. Key takeaways Morning ear soreness from earbuds is caused by sustained pressure on thin skin over cartilage with a limited blood supply. Simple pressure soreness fades within hours. A firm, painful lump that lasts weeks may be chondrodermatitis nodularis helicis (CNH) and needs a doctor's look. A red, hot, swollen outer ear with a normal ear...
Read more