What are GLP-1 Weight Loss Drugs?

Michael Albrecht, MD

Mar 19, 2025

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By the time patients get to me in weight management practice, they’ve often heard of the “GLP-1 drugs,” such as Ozempic, Mounjaro, Wegovy, Zepbound, and Saxenda. These are powerful medications that can help people lose weight by 15 to 20% or more of their starting weight. However, one of the most common questions I’m asked in weight loss clinic is: “How do these drugs work?”

After being asked that question, I usually go into my spiel of telling them that GLP-1 medications mimic a hormone that our bodies naturally make called GLP-1 (Glucagon-like Peptide 1). I then go on to tell them how GLP-1 works in our bodies:

The GLP-1 hormone is secreted by our small intestine into the bloodstream continuously by our intestines at low levels, but when we eat carbohydrates (“carbs”), our intestines detect this and secrete a “spike” of GLP-1 hormone into the bloodstream.

What does GLP-1 do after it’s in our bloodstream? First, GLP-1 stimulates the pancreas to increase production of insulin and decrease the production of another hormone called glucagon. The overall effect is to decrease our blood sugar levels. Second, GLP-1 tells the stomach to sloooow dooooown. Doctors call this effect “delayed gastric emptying.” In this way, GLP-1 makes the food we eat stay in our stomach longer, and this helps us feel full quicker. Third, GLP-1 has effects on the brain. It communicates to the brain that we’re not hungry, and thus, GLP-1 is a potent appetite suppressant.

GLP-1 drugs mimic the GLP-1 hormone because they bind to the same receptors as GLP-1 hormone in the body. Thus, these medications help us lose weight by increasing satiety (our sensation that we’re full after eating), and by suppressing appetite. Since the drugs also lower blood sugar, the medications also can be used to treat diabetes. We also have strong evidence that these medications reduce the risk for cardiovascular events such as heart attack and stroke.

These medications are very effective for weight loss. Studies have shown that it is common to experience weight loss of 15 - 20% or more of the initial body weight, depending on the medication.

Unfortunately, there’s always a catch. GLP-1 medications are very expensive and sometimes not covered by insurance. They also can cause side effects, such as nausea, vomiting, constipation, diarrhea, burping, heartburn, fatigue, injection site reactions, and hair loss. Caution is needed to use these medications with a prior history of pancreatitis or with any pre-existing gastrointestinal conditions, such as Crohns disease. Because of a theoretical risk of medullary thyroid cancer based on studies in rats, patients should not use these medications if there is a personal or family history of medullary thyroid cancer or a condition known as MEN 2 syndrome.

The bottom line is that the GLP-1 medications are very effective medications for weight loss. They have a number of positive effects in the body, but are not without side effects or expense. Discuss these medications further with your personal physician to help to understand if these medications are right for you.