If you are looking past semaglutide and tirzepatide, here is the short answer. The peptides with real weight-loss evidence are close relatives of those two. They mimic gut hormones, and each was tested in a large randomized trial. Several others sold for fat loss have little or no human data behind them.
A peptide is a short chain of amino acids, and what that means in practice is covered separately. Being a peptide says nothing about whether a molecule works. The trial record does. For the goal as a whole, start at the weight goal page.
Liraglutide: the older daily option
Liraglutide is a once-daily GLP-1 drug. The SCALE trial gave 3.0 mg a day or placebo to 3,731 adults without type 2 diabetes for 56 weeks [1]. Everyone also got lifestyle counseling.
People on liraglutide lost a mean of 8.4 kg. People on placebo lost 2.8 kg. At least 5% of body weight was lost by 63.2% on the drug and 27.1% on placebo. The most common side effects were mild or moderate nausea and diarrhea.
Retatrutide: three receptors at once
Retatrutide acts on three hormone receptors: GLP-1, GIP and glucagon. A phase 2 trial enrolled 338 adults with obesity for 48 weeks [2]. On the 12 mg dose, mean weight change was −24.2%, against −2.1% on placebo.
That is one mid-stage trial, not a full phase 3 program. Side effects were mostly stomach and bowel symptoms and rose with dose. Heart rate went up with dose, peaked at 24 weeks, then declined.
CagriSema: two peptides in one shot
CagriSema pairs semaglutide 2.4 mg with cagrilintide 2.4 mg, a peptide that mimics the hormone amylin. REDEFINE 1 randomized 3,417 adults without diabetes for 68 weeks [3].
Mean weight change was −20.4% on the combination and −3.0% on placebo. Stomach and bowel side effects hit 79.6% on the combination and 39.9% on placebo. Most were short-lived and mild to moderate.
Tesamorelin: belly fat, not body weight
Tesamorelin comes up in weight-loss searches because it reduces fat around the organs. In a trial of 412 people with HIV, that deep belly fat fell 15.2% on tesamorelin over 26 weeks and rose 5.0% on placebo [4].
Its FDA label is blunt about the limit. It says the drug is “not indicated for weight loss management as it has a weight neutral effect” [5]. The tesamorelin trials are covered in full elsewhere.
AOD-9604 and MOTS-c: almost no human data
These two are sold online for fat loss. The FDA’s own summary of what is known about them is stark [6].
For AOD-9604, the FDA says it has “no, or only limited, safety-related information.” It also notes serious adverse events that may be linked to it, though cause is unclear. For MOTS-c, the FDA says it has not found any human exposure data at all. The nominations to compound both of them were withdrawn.
MOTS-c came back for a July 2026 advisory meeting, reviewed for obesity. FDA’s briefing found no clinical studies or human exposure data by any route [7]. The committee still voted to recommend listing it [8]. That vote is not binding; listing would still require FDA rulemaking. The legal picture explains what that means.
What to take from this
The trade-off is simple to state. The peptides with the most weight lost also have the most side-effect data, because they were tested in thousands of people. The ones with no trials have no side-effect data either. That is a reason for caution, not a sign of safety.
If you are weighing options, ask a prescriber which of these has a trial in people like you. Then ask what the trial dose and length were.