GLP-1s and weight loss: How they work

Before you can learn how to read, you need to learn your ABCs. And before you decide to start taking a weight-loss drug like a GLP-1, you should learn how they actually work in your body. This article will get you there. It’s your plain-English guide to all things GLP-1s, including what they are and how they work. Ready to get knowledgeable?

GLP-1 stands for “glucagon-like peptide-1.” GLP-1 receptor agonists, which include semaglutide and liraglutide, work by mimicking the GLP-1 hormone that your body naturally releases in the gastrointestinal tract after eating. When you eat, your digestive system breaks down carbohydrates into simple sugars, which then enter your bloodstream. GLP-1 then triggers your pancreas to release insulin, which moves glucose out of your bloodstream and into cells to provide energy. 

GLP-1 medications mimic that hormone. So if you have type 2 diabetes, GLP-1 receptor agonists trigger your pancreas to release more insulin, which helps control blood sugar levels.

But GLP-1s affect your brain and stomach too. They target the appetite centers in your brain and delay stomach emptying, helping you to feel fuller for longer.

What are GLP-1/GIP agents?

Tirzepatide is a medication that is both a GLP-1 receptor agonist and also a GIP receptor agonist. GIP stands for glucose-dependent insulinotropic polypeptide. Both GLP-1 and GIP play a role in reducing appetite by stimulating neurons in the brain’s satiety center, and increasing insulin secretion in the pancreas.

You may know that GLP-1s are impactful, but how do GLP-1s help you lose weight? The short answer is: They make you less hungry. Here are the two main ways it does that. 

Appetite and reward pathways

GLP-1s work to influence the parts of your brain linked to appetite and food reward. The medication acts in the brain to reduce hunger. By targeting the brain’s dopamine reward system, they dampen the release of dopamine in the part of the brain tied to motivation, reward, and pleasure.

Fullness and slower gastric emptying

GLP-1s also slow gastric emptying, or make the stomach empty more slowly than normal. This can help you feel full for longer after meals, so you go longer between wanting to eat.

GLP-1s mimic how the natural hormone glucagon-like peptide-1 works in the body. It stimulates the pancreas to release insulin to move glucose into your cells for energy, which lowers blood sugar. It also stops the release of glucagon (a hormone that raises blood sugar).

Both gastric inhibitory polypeptide (GIP) and glucagon-like peptide are what’s called “primary incretin hormones” released into the bloodstream after you eat. They work by binding to their receptors, GIPR and GLP-1R.

Single-agonist GLP-1s include semaglutide and liraglutide, while tirzepatide is an example of a dual agonist GIP/GLP-1. Studies suggest that the dual agonist approach has more powerful benefits in terms of both glucose control and weight-reduction. 

How does Ozempic work?

Ozempic is a brand name for semaglutide — a single GLP-1 receptor agonist — FDA-approved for type 2 diabetes. This means it works to mimic one hormone in your body, GLP-1, to help regulate blood sugar levels and help you to feel less hungry. Wegovy is also a brand name for semaglutide and is FDA-approved for weight loss.

How does tirzepatide work?

As mentioned above, tirzepatide is a dual agonist. This means that it mimics two hormones: GIP and GLP-1. Tirzepatide is prescribed as Mounjaro, FDA-approved for type 2 diabetes, and Zepbound, FDA-approved for weight loss. The dual agonist maximizes weight loss compared to GLP-1 medications.

As with all aspects of healthcare, everyone’s different, and what works for one person may not work for another. That’s why it’s so important to seek personalized advice and support from your clinician throughout your weight-loss journey. They’ll be equipped to help you find the right path, based on individualized risk factors and medical history. 

Losing weight is both a physical and mental challenge, and it’s important to remember that weight changes typically occur gradually. Good habits require long-term maintenance and weight loss plateaus are common along the way. 

Alongside weight loss medications, track your protein, fiber, movement, and sleep quality. If you’re worried or frustrated about your weight-loss journey, speak to your clinician for support.

GLP-1 weight loss over time

Studies suggest that both semaglutide and tirzepatide can result in meaningful weight loss. For example, after a little more than a year of treatment, average weight loss is around 15% to 21%, depending on the medication.

Everyone’s weight loss journey is different, but you may start to notice changes in the first few months. One study suggested that participants using semaglutide saw weight loss of around 5% after three months.

As with any medication, there are certain side effects of GLP-1s to be aware of. Luckily, these effects usually improve as your body adjusts to the new medication. In most instances, your clinician will start off on a lower dose and then increase it slowly to minimize the chance of side effects.

Not everyone experiences major side effects.  But here’s a GLP-1 side effect overview to familiarize yourself with:

• Abdominal discomfort

• Vomiting

• Diarrhea

• Constipation

• Nausea

While the list above features the most common side effects, some people may experience:

• Headaches 

• Fatigue

• Dizziness

• Increased heart rate

You may also notice redness or stinging at the injection site.

GLP-1 medications are considered generally safe, but it’s important to be aware of risks. Gastrointestinal side effects may lead to an increased risk of dehydration, kidney concerns, or malnutrition.

Your clinician will advise against taking a GLP-1 medications if you:

• Are pregnant

• Breastfeeding 

• Have a serious gastrointestinal condition

• Have a personal or family history of MEN2/MTC

As always, if you’re experiencing any severe or persistent symptoms, speak to your clinician. It’s also always best to be safe and speak to a healthcare professional if you have any worries or concerns about your medication.

Weight Watchers works to support behavior change alongside weight-loss medication. From food planning and activity goals to coaching and accountability support, we’re here to help you build weight loss habits to achieve lasting change. 

We bring together science, guidance, and support — with or without medication. Find out more about our programs.

GLP-1 medications work by mimicking hormones that your body naturally produces. They help regulate blood sugar and increase how long you feel full after you eat, as well as target appetite centers in your brain. Together, this can help reduce your eating and result in weight loss.

Under a clinician's advice, paired with sustainable habits and professional guidance, GLP-1 medications may lead you to progress towards your weight-loss goals.