GLP-2 vs GLP-1: siblings, not versions

The names make it look like a sequence: GLP-1, then GLP-2, then something better. In reality the two peptides were numbered in the order they were found inside the same precursor protein. They are released together, from the same cell, after the same meal. Then they go to different receptors and do different things.

What they share

Both are cut from proglucagon, the protein that also gives rise to glucagon in the pancreas. In the gut, L cells process proglucagon into GLP-1 and GLP-2 and release them together after eating. L cells are concentrated in the terminal ileum and colon. Both peptides are broken down quickly by the enzyme DPP-4, which is why every drug in either class is a modified version built to last longer than the natural peptide. Both slow stomach emptying.

Where they split

The GLP-2 receptor was cloned in 1999. Cells expressing it responded to GLP-2 but not to GLP-1 or related peptides, and the receptor was found mainly in the gastrointestinal tract. The GLP-1 receptor is found in the pancreas, the stomach, the heart and, importantly for weight, in appetite centres of the brain. That difference in where the receptor lives explains almost every difference that follows.

A shared enzyme, and a side door

Because DPP-4 breaks down both peptides, blocking it raises both. That is how the DPP-4 inhibitor tablets for type 2 diabetes, the gliptins, work on the GLP-1 side. In rats and mice, a DPP-4 inhibitor given with GLP-2 roughly doubled the level of intact GLP-2 for the first hour and markedly increased the growth of the small bowel compared with GLP-2 alone. In mice, a fifth of the GLP-2 dose plus the inhibitor matched the growth from the full dose. That is animal work. It shows how closely the two peptides are tied at the level of their breakdown, even though their receptors and jobs are separate.

Why GLP-2 is not a weight loss drug

Three lines of evidence point the same way.

• No appetite effect. In a randomised, blinded, placebo-controlled crossover study of 18 healthy normal weight adults, a 4.5 hour GLP-2 infusion did not change appetite ratings, the palatability of the meal or how much people ate. The authors concluded that circulating GLP-2 "does not seem to play a significant role in human appetite regulation".
• Weight goes up, not down, in the people who take it. In eight short bowel patients given GLP-2 for 35 days, body weight rose 1.2 kg, lean body mass rose 2.9 kg and fat mass fell 1.8 kg. The point of the treatment is to absorb more of what is eaten.
• The receptor is in the wrong place. The appetite effect of GLP-1 drugs depends on receptors in the brain. The GLP-2 receptor is mainly a gut receptor.

The one place the two meet in weight research is dual agonists: single molecules that hit both the GLP-1 and GLP-2 receptors. The weight loss in those trials comes from the GLP-1 side; the GLP-2 side was added in the hope of improving the gut barrier and inflammation. The only one to reach published human results, dapiglutide, was paused by its developer in November 2025.

How the drug classes compare in practice

The GLP-1 class is weekly or daily, dosed in fixed steps, and judged by kilograms and HbA1c. In STEP 1, semaglutide 2.4 mg produced a mean weight loss of 14.9% at 68 weeks against 2.4% on placebo. The GLP-2 class is dosed by body weight (teduglutide is 0.05 mg per kg a day) and judged by litres of intravenous support given up. In STEPS, teduglutide cut weekly support by 4.4 litres against 2.3 on placebo. Different units, different diseases, different specialists: endocrinology and obesity medicine on one side, intestinal failure teams on the other.

Opposite concerns about the gut

GLP-1 drugs are known for nausea, vomiting and slowed stomach emptying; the GLP-1 side effects page has the trial rates. GLP-2 drugs have a different signature. Because they make intestinal tissue grow, their labels focus on growth: the teduglutide label warns of "acceleration of neoplastic growth", requires a colonoscopy before starting and after the first year, and calls for the drug to be stopped if a gastrointestinal cancer is found. It also warns of intestinal obstruction, gallbladder and pancreatic problems, and fluid overload as absorption improves. The teduglutide page covers the full label.

The naming trap

Online, "GLP-2" is often used to mean tirzepatide and "GLP-3" to mean retatrutide, as if each were the next generation of GLP-1. Neither drug acts on the GLP-2 receptor. Tirzepatide is a GIP and GLP-1 receptor agonist; retatrutide adds the glucagon receptor. The slang page explains where the labels came from, and the GLP-1 hub covers the drugs themselves.

Which section you need

If you are interested in weight, blood sugar or the drugs called Ozempic, Wegovy, Mounjaro or Zepbound, you want the GLP-1 section and the four-way comparison. If you or someone you care for has short bowel syndrome or intestinal failure, you want this section, starting with what is GLP-2 and short bowel syndrome and GLP-2.

Logging either one

The two classes are tracked differently. GLP-1 users tend to log weekly doses, weight and side effects; GLP-2 users log daily injections, intake, output and labs. Peptide AI's dose log, nutrition tracking and bloodwork tracking put any of those on one timeline.