Short answer: GLP-1 weight-loss injections are prescription injectable medications that mimic the gut hormones GLP-1 (glucagon-like peptide-1) and GIP. They quiet the appetite center in the brain, slow stomach emptying and help balance blood sugar. The main active ingredients are tirzepatide (Mounjaro) and semaglutide (Wegovy, Ozempic).

Key takeaways

  • By mimicking the GLP-1 hormone, they create a feeling of fullness in the brain and delay stomach emptying.
  • In clinical trials (SURMOUNT and STEP), average weight loss of 15% to 22% of body weight was observed.
  • They are injected weekly under the skin (abdomen, thigh, arm).
  • All weight-loss injections require a prescription and should be used under a doctor's supervision.

"Weight-loss injection" is the everyday name for GLP-1 receptor agonist medications. These medications mimic GLP-1, a hormone the gut releases naturally: they prolong the feeling of fullness, slow stomach emptying and reduce appetite. As a result, people eat less and lose weight over time. All of them require a prescription and medical follow-up.

This page is for general information only and is not medical advice. Decisions about medication use, dose and duration belong to your doctor alone.

How do they work?

GLP-1 is a hormone the gut releases after you eat. It sends a "I'm full" signal to the brain, regulates insulin release from the pancreas and slows the emptying of the stomach. Weight-loss injections mimic this hormone's effect and produce the same signals for much longer.

The newer-generation medication tirzepatide (Mounjaro, Zepbound) also acts on the receptor of a second hormone called GIP. In clinical trials, weight-loss results for this dual-action group were higher than for medications that act on GLP-1 alone.

Which weight-loss injections are there?

The best-known products and their active ingredients:

Mounjaro

Active ingredient: tirzepatide. Given once a week. Acts on both the GIP and GLP-1 receptors.

Zepbound

Active ingredient: tirzepatide. The same molecule as Mounjaro, offered under a separate name with a weight-management indication.

Ozempic

Active ingredient: semaglutide. Given once a week. Its primary indication is type 2 diabetes.

Wegovy

Active ingredient: semaglutide. The same molecule as Ozempic, offered with a different dosing schedule for weight management.

Saxenda

Active ingredient: liraglutide. Unlike the others, it is given once a day.

Trulicity

Active ingredient: dulaglutide. Given once a week; its indication is type 2 diabetes.

Two products with the same active ingredient (for example, Ozempic and Wegovy) come with different dose steps and different indications. Which one is right for you is a medical decision.

To see the active ingredient, dosing frequency and indication of all six products side by side, see GLP-1 medication names and comparison table.

How are they given?

These medications are injected under the skin (subcutaneously). The usual sites are the abdomen, the front of the thigh and the outer upper arm. Choosing a different site each time is recommended; injecting into the same spot again and again can cause hardening of the skin and changes in absorption.

Treatment usually starts at the lowest dose and is increased step by step under medical supervision as your body adjusts. This gradual increase is called titration, and it is done to reduce side effects.

What should you watch for?

  • All of them require a prescription; they should not be used without a doctor's evaluation.
  • Products sold without a prescription or online may be counterfeit and carry serious risks.
  • The most common side effects are nausea, constipation, diarrhea and loss of appetite.
  • The cold chain matters; storage conditions are listed in the package leaflet.
  • Adequate protein and regular movement are recommended to preserve muscle mass.

Which symptoms are expected and which call for seeing a doctor without delay are covered on a separate page: GLP-1 injection side effects and risks.

Tracking your treatment

On a weekly injection schedule, the hardest part is remembering what happened last week: which day you injected, which site you used, how your weight moved, which day you had nausea. These are exactly the things your doctor asks at a follow-up visit.

Haftra is a free iPhone app built to keep this tracking in one place. It records your injection day and site rotation, your weight trend and your side effects; you can use it without creating an account, and then your records stay on your phone. It does not suggest doses or make diagnoses; it simply puts your own observations in order.

iPhone, iPad and Apple Watch. Free.

Frequently asked questions

How exactly do weight-loss injections make you lose weight?

They activate fullness receptors in the hypothalamus region of the brain and lengthen stomach emptying time, so you stay full longer on smaller portions.

How many times a week is a weight-loss injection given?

Mounjaro, Zepbound, Ozempic and Wegovy are given once a week. Saxenda is used once a day. Your doctor decides the frequency and the dose.

Who are weight-loss injections prescribed for?

They are generally prescribed by a doctor for people with obesity who have a body mass index (BMI) of 30 or above, or for people with a BMI above 27 who also have a condition such as high blood pressure or diabetes.

Who should not use them?

They are not used, or need special evaluation, in situations such as pregnancy, breastfeeding, a history of certain thyroid cancers or a history of pancreatitis. Deciding whether they are suitable is an evaluation only a doctor can make.

Can you get a weight-loss injection without a prescription?

No. All of them require a prescription. Sources that sell them without one are not reliable; the risk of counterfeit products is real and can have serious consequences.

Do you regain weight when you stop the medication?

Clinical trials show that part of the weight lost can be regained after treatment stops. That is why it matters to build eating and activity habits during treatment. The decision to stop should be made together with your doctor.

Are weight-loss injections a permanent solution?

The medication provides biological support for fullness; for lasting weight control, building healthy eating and physical activity habits during treatment is essential.

In-depth pages

Sources

  • NHS - Obesity treatment
  • U.S. Food and Drug Administration (FDA)

Last reviewed: August 2, 2026