If diet and exercise alone haven’t moved the scale, you’re not imagining it. Your body fights weight loss with hunger hormones and a slower metabolism. Weight loss injections work on that biology directly, which is why they’ve changed how doctors treat obesity.
This guide explains how weight loss injections work, what results to expect, the side effects, what happens when you stop, and how to tell brand-name medications from compounded versions.
| The short answer: what are weight loss injections? Weight loss injections are prescription medications, mainly semaglutide (Wegovy) and tirzepatide (Zepbound), usually injected once a week. They mimic gut hormones that reduce appetite and slow digestion. In major trials, people lost about 15% to 21% of their body weight on average over 68 to 72 weeks when combined with diet and activity. They’re FDA-approved for adults with a BMI of 30 or more, or 27 or more with a weight-related health condition. |
Key Takeaways
- Semaglutide and tirzepatide are the most effective FDA-approved options available today.
- Average results in trials ranged from about 15% to 21% of body weight, depending on the drug and dose.
- Stomach-related side effects are common, especially while the dose is increasing.
- Some of the weight you lose can be lean mass, so protein and strength training matter.
- Most people regain much of the weight if they stop without a plan.
- Compounded versions are not the same as FDA-approved products, and the rules around them tightened in 2025.
How Do Weight Loss Injections Work?
Most of these medications copy GLP-1 (glucagon-like peptide-1), a hormone your gut releases after you eat. Tirzepatide also mimics a second gut hormone called GIP. Together, these signals:
- Tell your brain you’re full sooner, so you eat less without constant willpower
- Slow how quickly your stomach empties, so fullness lasts longer
- Help your body release insulin when blood sugar rises
- Quiet the “food noise” many people describe, such as constant cravings
The medication doesn’t burn fat on its own. It makes eating less much easier to sustain, which is what drives the weight loss.
FDA-Approved Weight Loss Injections Compared
FDA-approved options at a glance (as of October 2026)
| Medication | Active ingredient | How often | Average weight loss in key trial |
| Wegovy | Semaglutide 2.4 mg | Once weekly | 14.9% at 68 weeks (STEP 1), vs. 2.4% with placebo |
| Wegovy HD | Semaglutide 7.2 mg | Once weekly | 20.7% at 72 weeks if taken as directed; 18.7% counting everyone (STEP UP) |
| Zepbound | Tirzepatide 5, 10 or 15 mg | Once weekly | 15% to 20.9% at 72 weeks by dose, vs. 3.1% with placebo (SURMOUNT-1) |
| Saxenda | Liraglutide | Once daily | Smaller average loss than the weekly options |
Sources: STEP 1, STEP UP, SURMOUNT-1.
Wegovy HD, a higher 7.2 mg dose of semaglutide, was approved in March 2026. Not a fan of needles? Two pills are now FDA-approved too: the Wegovy pill (oral semaglutide), approved in December 2025, and Foundayo (orforglipron), approved in April 2026. Foundayo’s highest dose produced 11.2% average weight loss in its main trial (ABC7).
Who Is a Good Candidate for Weight Loss Injections?
FDA approval covers adults with obesity (a BMI of 30 or higher) or overweight (a BMI of 27 or higher) with at least one weight-related condition, such as high blood pressure, type 2 diabetes, high cholesterol or sleep apnea (Zepbound label).
These medications aren’t right for everyone. You likely shouldn’t use them if you:
- Have a personal or family history of medullary thyroid cancer or MEN 2 syndrome
- Are pregnant, trying to conceive or breastfeeding
- Have severe gastroparesis (very slow stomach emptying)
- Have had a serious allergic reaction to the medication
A history of pancreatitis, gallbladder disease, kidney problems or diabetic eye disease doesn’t always rule you out, but it needs a careful review first.
What Results Can You Expect, and How Fast?
Treatment starts at a low dose that steps up gradually over several months. This helps your body adjust and keeps side effects manageable. Weight usually comes off steadily over the first year, and the headline trial results above were measured at 68 to 72 weeks.
Results vary widely. In STEP 1, 86.4% of people on semaglutide lost at least 5% of their body weight, compared with 31.5% on placebo (ACC). Even 5% matters: it’s often enough to improve blood pressure, blood sugar and joint pain.
GLP-1 medications also bring benefits beyond the scale. In the SELECT trial, semaglutide cut the combined risk of heart attack, stroke and cardiovascular death by 20% in people with obesity and heart disease, which led to a heart-protection approval for Wegovy (CNBC). Zepbound is also approved to treat moderate to severe obstructive sleep apnea in adults with obesity.
Side Effects and Safety of Weight Loss Shots
The most common side effects are digestive and tend to appear while your dose is going up:
- Nausea, vomiting or diarrhea
- Constipation, bloating or acid reflux
- Belly pain or burping
- Fatigue and injection site reactions
Most cases are mild to moderate. In STEP 1, 4.5% of people stopped semaglutide because of digestive side effects, compared with 0.8% on placebo (ACC).
Less common but serious risks
- Pancreatitis. Severe, persistent belly pain needs prompt medical attention.
- Gallbladder problems, including gallstones.
- Kidney injury, usually from dehydration after vomiting or diarrhea.
- Low blood sugar, mainly if you also take insulin or a sulfonylurea.
- Aspiration during anesthesia. Tell your surgeon or dentist you’re on a GLP-1 before any sedation.
These medications carry a boxed warning because they caused thyroid C-cell tumors in rats. It’s not known whether that happens in people (Zepbound label). Women taking tirzepatide with birth control pills should use a backup method for 4 weeks after starting and after each dose increase, because slower digestion can make the pill less reliable.
Will You Lose Muscle on a GLP-1?
Some. In body scans from the major trials, lean mass made up about 38% to 39% of weight lost on semaglutide in STEP 1, and about 25% on tirzepatide in SURMOUNT-1 (Barbell Medicine). Those scans also count water and organ tissue as lean mass, so actual muscle loss is likely smaller. It still matters, because muscle supports your metabolism, strength and long-term results.
Dr. Whitney Elsesser, DNP, CNM, our wellness provider, puts it simply: a GLP-1 can curb your appetite, but it can’t put protein on your plate or build muscle for you. That’s why our programs treat protein and strength training three to four times a week as core parts of the plan.
- Prioritize protein. Aim for about 1.2 to 1.6 g per kg of body weight per day, unless your provider advises otherwise.
- Lift weights. Train major muscle groups with progressive resistance several times a week.
- Sleep 7 to 9 hours. Recovery is when muscle repairs.
- Track more than the scale. Waist size, strength and body composition tell the real story.
Want extra support? Emsculpt Neo targets muscle and fat without downtime. Read the science behind Emsculpt Neo or our honest take on peptides for muscle growth.
What Happens When You Stop?
Obesity is a chronic condition, and the medication works only while you take it. In the STEP 1 extension, people who stopped semaglutide regained about two-thirds of the weight they’d lost within a year. Most of their improvements in blood pressure, blood sugar and cholesterol also faded (STEP 1 extension).
That doesn’t mean you’re locked in forever. It means stopping should be a planned step with your provider, with strong habits, muscle-building and ongoing support in place first.
Brand-Name vs. Compounded Weight Loss Injections
During the drug shortages that began in 2022, compounding pharmacies were allowed to make copies of semaglutide and tirzepatide. FDA declared those shortages over in December 2024 for tirzepatide and February 2025 for semaglutide. After the grace periods ended in 2025, pharmacies can generally compound these drugs only when a prescriber documents a clinically significant difference for an individual patient. FDA has sent warning letters to telehealth sellers through 2026 for marketing compounded versions as if they were the approved drugs (Health Law Alliance).
Compounded medications aren’t FDA-approved, which means FDA hasn’t reviewed their safety, effectiveness or quality. Before you start any weight loss injection, ask:
- Is this an FDA-approved brand-name product or a compounded medication?
- If it’s compounded, which licensed pharmacy makes it, and why is a compounded version medically needed for me?
- How is my dose measured and adjusted?
Why Hormones Can Make or Break Your Results
If you’re doing everything right and still stalling, Dr. Whitney looks at hormones first. Estrogen and testosterone affect where your body stores fat, how easily you build muscle and how much energy you have to stay consistent.
That’s why a complete weight loss plan often includes hormone testing. Learn more about bioidentical hormone replacement therapy, hormone therapy for women, or read our guide to men’s health blood work.
Weight Loss Injections in Stratham, NH
At About Face — A Well Labs+ Medspa, our medically guided weight loss program starts with a comprehensive consultation covering your medical history, lifestyle and goals. Your plan can combine prescription weight loss medications, including GLP-1s, with hormone optimization, nutrition guidance and ongoing monitoring. We adjust your plan as you progress, so results are safe and built to last.
Explore all of our wellness services or read about the benefits of medical weight loss programs. We welcome patients from Stratham, Portsmouth, Exeter and across the New Hampshire Seacoast at 64 Portsmouth Ave, Suite 4. Meet our team, book a virtual consultation, or call (603) 580-5296.
| Ready to lose weight with medical support that protects your muscle and your results? Book your weight loss consultation at About Face — A Well Labs+ Medspa in Stratham today. |
Frequently Asked Questions
How much weight can you lose with weight loss injections?
In major trials, average weight loss was about 15% of body weight with semaglutide 2.4 mg, up to about 21% with the highest dose of tirzepatide, and about 19% to 21% with semaglutide 7.2 mg, measured over 68 to 72 weeks. Individual results vary widely.
Which is better, semaglutide or tirzepatide?
In separate trials, the highest dose of tirzepatide produced more average weight loss than semaglutide 2.4 mg. The best choice depends on your health history, side effects, insurance coverage and how your body responds, so it’s a decision to make with your provider.
Are weight loss injections safe?
For appropriate candidates under medical supervision, they’re considered safe and effective. Digestive side effects are common, and rare serious risks include pancreatitis and gallbladder problems. They aren’t used in people with a personal or family history of medullary thyroid cancer or MEN 2.
Do I have to take weight loss injections forever?
Not necessarily, but most people regain weight after stopping. In the STEP 1 extension, people regained about two-thirds of their lost weight within a year. Any plan to stop should be gradual and supported by strong habits.
Will I lose muscle on a GLP-1?
Some of the weight lost can be lean mass. Eating enough protein and doing regular strength training helps protect muscle while you lose fat.
Are compounded weight loss injections the same as Wegovy or Zepbound?
No. Compounded versions aren’t FDA-approved, and since the shortages ended in 2025, pharmacies can generally compound them only when there’s a documented clinical reason for an individual patient. Always ask exactly what you’re being prescribed.
Can I use birth control pills while taking a GLP-1?
With tirzepatide, use a non-oral method or add a backup method for 4 weeks after starting and after each dose increase, because the medication can make birth control pills less effective. Talk to your provider about your situation.