Peptides for Weight Loss: Which Ones Work Best (and Are Prescribed)?

How Do Weight-Loss Peptides Work?

Peptides are short chains of amino acids that act as biological messengers in the body. Some influence appetite, metabolism, and fat storage, making them a focus in obesity treatment.

The most important group for weight loss is GLP-1 receptor agonists such as semaglutide and liraglutide. These peptides mimic the natural gut hormone glucagon-like peptide-1 (GLP-1), which:

• Slows gastric emptying, keeping food in the stomach longer.

• Enhances satiety signals in the brain, helping people feel full sooner and for longer.

• Regulates blood sugar by triggering insulin release after meals.

This mechanism has been validated in clinical trials. For example, in the STEP 1 trial, patients taking semaglutide lost an average of 14.9% of their body weight over 68 weeks, compared with just 2.4% in the placebo group (NEJM study).

Other peptides like CJC-1295 or AOD-9604 are marketed for fat loss, but unlike GLP-1 drugs, they lack robust human data and are not FDA-approved for obesity (FDA warning on unapproved peptides).

Do Peptides Really Work for Weight Loss?

Yes, but only certain peptides with clinical approval have been proven effective. Others are either experimental or marketed without sufficient evidence.

Prescription GLP-1 and GIP/GLP-1 Peptides

• Semaglutide (Ozempic, Wegovy) and liraglutide (Saxenda) are FDA-approved and have demonstrated significant weight reduction in large randomized controlled trials. In the STEP 1 trial, semaglutide led to an average 14.9% reduction in body weight over 68 weeks, far outperforming placebo (NEJM study on semaglutide for weight loss).
• Tirzepatide (Mounjaro, Zepbound), a dual GIP/GLP-1 receptor agonist, has shown even greater results. In the SURMOUNT-1 trial, participants lost up to 22.5% of body weight over 72 weeks (study on tirzepatide in obesity).

Clinic-Marketed Peptides

Peptides like CJC-1295, Ipamorelin, and AOD-9604 are often advertised by anti-aging or weight loss clinics.

• Human trials specifically examining fat loss are limited or absent.
• The FDA has not approved these peptides for obesity treatment (FDA guidance on unapproved peptides).
• Claims of fat burning largely come from animal data or small, non-peer-reviewed studies.

Which Peptides Are Proven to Work Best for Weight Loss?

When it comes to peptides that genuinely help with weight loss, the strongest evidence lies with FDA-approved prescription medications. These belong to a class of drugs called incretin mimetics, which either mimic or enhance the effects of gut hormones that regulate appetite and metabolism.

Three stand out as the most effective semaglutide, liraglutide, and tirzepatide.

Semaglutide (Ozempic, Wegovy, Rybelsus)

Semaglutide is a GLP-1 receptor agonist available under brand names such as Ozempic (for type 2 diabetes), Wegovy (for obesity), and Rybelsus (an oral form). It works by slowing gastric emptying and enhancing satiety signals, which leads to reduced calorie intake. In the pivotal STEP 1 clinical trial, participants who received weekly semaglutide injections lost an average of 14.9% of their body weight over 68 weeks, compared with 2.4% in the placebo group (study in the New England Journal of Medicine).

This makes semaglutide one of the most effective prescription options currently available.

Liraglutide (Saxenda, Victoza)

Liraglutide is another GLP-1 agonist, marketed as Saxenda for weight management and Victoza for type 2 diabetes. Unlike semaglutide, which is given weekly, liraglutide requires a daily injection. While it is less potent than semaglutide, it has still shown clinically meaningful results. In clinical trials, patients using liraglutide typically lost around 5–8% of their body weight, compared to placebo groups (FDA approval summary for Saxenda).

Liraglutide paved the way for GLP-1 therapies in obesity treatment, but most patients and clinicians now prefer semaglutide or tirzepatide because of stronger results and easier dosing.

Tirzepatide (Zepbound, Mounjaro)

Tirzepatide is the newest entrant in this category and represents a significant advance because it activates both GLP-1 and GIP receptors. This dual action amplifies its effects on appetite regulation and glucose metabolism. In the SURMOUNT-1 trial, people treated with tirzepatide lost up to 22.5% of their body weight over 72 weeks, making it even more effective than semaglutide (NEJM tirzepatide study).

It is sold as Mounjaro for diabetes and Zepbound for obesity, both requiring a doctor’s prescription.

Are CJC-1295, Ipamorelin, and AOD-9604 Effective for Weight Loss?

Some peptides are heavily promoted by anti-aging and weight loss clinics, including CJC-1295, Ipamorelin, and AOD-9604, but unlike semaglutide or tirzepatide, they are not FDA-approved for obesity and lack strong clinical evidence. CJC-1295 and Ipamorelin are designed to stimulate growth hormone release and are often marketed for fat loss or used together as a “stack,” yet no large human trials confirm they cause meaningful weight reduction.

AOD-9604, sometimes called the “fat-burning peptide,” showed limited promise in animal studies but has failed to demonstrate consistent results in people, leading the FDA to explicitly state it is not an approved treatment (FDA on unapproved drugs). While clinics may market these compounds aggressively, their benefits remain unproven and their safety uncertain.

Do You Need a Prescription for Weight-Loss Peptides?

A prescription is always required. Medications like semaglutide (Ozempic, Wegovy), liraglutide (Saxenda), and tirzepatide (Mounjaro, Zepbound) can only be obtained through a licensed healthcare provider because they are FDA-approved drugs that must be prescribed and monitored by a physician. This ensures correct dosing, proper screening for contraindications, and monitoring of side effects.

Peptides such as CJC-1295, Ipamorelin, and AOD-9604 are not approved for medical use in weight management and should not be sold as prescription therapies. The FDA has issued repeated warnings about companies marketing unapproved peptides as “research chemicals” or selling them directly to consumers online (FDA warning on unapproved drugs). These unregulated products may contain inaccurate doses, contaminants, or entirely different substances, creating unnecessary ris

Are Peptides Safe? 

The most common side effects are gastrointestinal issues, including nausea, vomiting, diarrhea, and constipation. In most cases, these symptoms are mild to moderate and improve over time, but they can be severe enough for some patients to discontinue treatment (semaglutide STEP 1 trial results).

There are also rarer risks. GLP-1 drugs have been linked to increased risk of gallbladder disease, and they carry warnings about possible associations with pancreatitis. Animal studies have suggested a potential link to thyroid tumors, though this has not been proven in humans (FDA prescribing information for Wegovy). For this reason, people with a personal or family history of certain thyroid cancers are advised not to use these medications.

Who Should Consider or Avoid Peptide Therapy?

Not everyone is a good candidate for peptide-based weight-loss treatments. The prescription peptides semaglutide, liraglutide, and tirzepatide are generally intended for people with a body mass index (BMI) of 30 or higher, or a BMI of 27 or higher with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnea (FDA Wegovy prescribing information). These medications are most beneficial for patients who have struggled to lose weight through lifestyle measures alone and who need a medical approach to support long-term results.

On the other hand, there are groups that should avoid peptide therapy altogether. People with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN2) should not use GLP-1 receptor agonists because of potential tumor risks observed in animal studies. Caution is also advised for patients with a history of pancreatitis or severe gastrointestinal disorders. Pregnant or breastfeeding individuals are generally not prescribed these medications due to safety concerns (FDA Wegovy safety warnings).

Where can I get peptide therapy for weight loss in Manhattan?

Peptide-based weight-loss treatments such as semaglutide (Wegovy) and tirzepatide (Zepbound) are only available by prescription. If you’re in Manhattan, the safest option is to consult with a licensed medical clinic that specializes in obesity care. These clinics can provide medical evaluation, prescribe FDA-approved peptides when appropriate, and monitor your progress. Avoid online vendors or gyms offering unapproved peptides, as these products may be unsafe.

How much does peptide therapy cost in Manhattan?

The cost of peptide therapy can vary depending on the medication and your insurance coverage. FDA-approved options like semaglutide and tirzepatide can cost over $1,000 per month without insurance, but some plans may cover part of the expense if prescribed for obesity or diabetes. Clinics in Manhattan typically offer consultations to help you understand costs upfront, including whether compounded or branded medications are appropriate for you.

What Questions to Ask Your Doctor

Before starting peptide therapy, patients should go into the consultation prepared with key questions.

Here are the most important ones to consider

• Which peptides are FDA-approved and appropriate for me?
  Confirm whether you are being offered a proven prescription option (such as semaglutide, liraglutide, or tirzepatide) rather than an unapproved clinic-marketed peptide.
• What side effects should I expect?
  Ask about common gastrointestinal issues (nausea, vomiting, diarrhea) and rarer risks like gallbladder disease or pancreatitis (FDA Wegovy prescribing information).
• How long would I need to stay on this medication?
  Clinical studies show that stopping GLP-1 therapy often leads to weight regain (STEP 4 trial on semaglutide withdrawal), so it’s important to understand the long-term plan.
• What will this cost, and is it covered by insurance?
  These medications can be expensive; coverage varies by insurance plan and provider.
• Can peptide therapy be combined with other weight-management strategies?
  Ask how diet, exercise, or behavioral support will be integrated alongside medication for the best long-term results.

Frequently Asked Quesitons

Do peptides cause muscle loss along with fat loss?

Yes. Clinical studies show that while GLP-1 peptides like semaglutide and tirzepatide primarily reduce fat mass, some lean muscle is lost as well. This is a common effect of rapid weight reduction, regardless of method. To help preserve muscle, patients are advised to combine peptide therapy with resistance training and adequate protein intake (STEP 1 body composition analysis).

Can peptides be stacked together for better results?

No clinical evidence supports “stacking” peptides for weight loss. Combinations such as CJC-1295 with Ipamorelin are marketed by some clinics, but they have not been proven effective in controlled human studies. FDA-approved peptides like semaglutide or tirzepatide are designed to be used individually under medical supervision.

Are compounded peptides safe to use instead of brand-name medications?

Compounded peptides are sometimes offered when branded medications are expensive or in short supply, but the FDA has warned that compounded semaglutide and tirzepatide may not meet the same safety or quality standards as FDA-approved products (FDA statement on compounded semaglutide). Patients should verify whether their clinic dispenses approved drugs or compounded alternatives.

What happens if I stop peptide therapy suddenly?

Discontinuing peptide therapy often leads to weight regain. In the STEP 4 trial, participants who stopped semaglutide regained about two-thirds of the weight they had lost within one year (STEP 4 withdrawal study). This shows that peptides are most effective when part of a long-term plan, ideally supported by lifestyle changes.

Is it safe to buy peptides online without a prescription?

No. The FDA has issued multiple warnings that peptides sold online as “research chemicals” may be contaminated, mislabeled, or entirely unsafe. Legitimate peptide therapy for weight loss should always come from an FDA-approved medication prescribed by a licensed healthcare provider (FDA guidance on unapproved drugs).