Peptides are short chains of amino acids, the same building blocks that make up proteins. They occur throughout the body and participate in a wide range of biological processes. The main distinction between a peptide and a protein is length and structure: peptides are generally made up of two to fifty amino acids linked together, while proteins are larger, more complex molecules often formed from multiple folded peptide chains.
Peptides exist naturally in the human body, where they are produced by cells to carry out specific signaling functions. Scientists have also learned to synthesize peptides in laboratory settings, opening the door to both cosmetic applications (topical skincare formulations) and therapeutic ones (compounded medications prescribed for specific health goals).
What Are Peptides Made Of?
Peptides are built from amino acids, which are small organic molecules containing an amino group, a carboxyl group, and a side chain that determines the amino acid’s identity. When two or more amino acids link together through what is known as a peptide bond, they form a chain. Short chains (roughly two to twenty amino acids) are usually called peptides, while longer chains (fifty or more) are generally classified as polypeptides or proteins.
The specific sequence and number of amino acids in a peptide determine its three-dimensional shape and its biological function. This is why even small changes to a peptide’s structure, such as swapping a single amino acid, can significantly change how it interacts with receptors in the body.
What Do Peptides Do in the Body?
Peptides function primarily as signaling molecules, meaning they relay information between cells and tissues. Research has explored several roles peptides may play in the body, including:
- Hormone regulation- Many hormones, including insulin and growth hormone-releasing hormone, are themselves peptides or are closely related to peptide structures.
- Cell communication and repair- Some peptides appear to be involved in processes related to tissue maintenance and cellular signaling pathways.
- Immune system modulation- Certain peptides interact with immune cells and may play a role in how the body responds to pathogens or inflammation.
- Metabolic regulation- Peptide hormones such as GLP-1 and GIP are involved in regulating appetite, insulin secretion, and glucose metabolism.
It’s worth noting that the specific function of any given peptide depends heavily on its structure and the receptors it interacts with. Research in this area continues to evolve, and scientists are still working to map out the full range of roles peptides play across different body systems.
Peptides in Medicine Today: The Numbers
Peptide-based medicine has moved from a niche research area to a fast-growing part of pharmaceutical development. A few figures illustrate the pace of that growth:
- According to Mordor Intelligence, the global peptide therapeutics market was valued at an estimated USD 49.68 billion in 2026 and is projected to reach USD 70.20 billion by 2031, a compound annual growth rate of 7.16%.
- In the STEP 1 trial, a Phase 3 randomized controlled trial in 1,961 adults with obesity or overweight-related comorbidities, participants receiving semaglutide saw a mean body weight reduction of 14.9% at 68 weeks, compared with 2.4% in the placebo group.
- In the SURMOUNT-1 trial, a Phase 3 randomized controlled trial in 2,539 adults with obesity or overweight-related comorbidities, mean body weight reductions ranged from 16.0% to 22.5% across tirzepatide dose groups at 72 weeks, compared with 2.4% for placebo.
These figures describe study-level averages for FDA-approved formulations of these medications, not individual outcomes, and compounded versions of these peptides have not independently undergone the same FDA review. Here is a list of Best weight loss medications that actually work.
Types of Therapeutic Peptides Used in Medicine
Peptides used in a medical context generally fall into a few broad categories, based on the physiological systems they’re studied in relation to:
GLP-1 and Dual-Agonist Peptides
GLP-1 receptor agonists, such as semaglutide, and dual GIP/GLP-1 agonists, such as tirzepatide, have been studied in large Phase 3 randomized controlled trials for their role in weight management and glucose regulation. Celia offers semaglutide oral tablets and tirzepatide oral tablets as compounded prescription formulations.
The STEP 1 and SURMOUNT-1 figures above come from the pivotal Phase 3 trials for these medications. These trials studied the FDA-approved versions of semaglutide and tirzepatide; compounded formulations have not independently undergone this same FDA review process. The table below summarizes both trials side by side.
| Trial | Study Type / Population | What Was Reported |
| STEP 1
(semaglutide) NCT03548935 |
Phase 3 RCT; n=1,961 adults with obesity or overweight-related comorbidities | Mean body weight reduction of 14.9% at 68 weeks vs. 2.4% with placebo |
| SURMOUNT-1
(tirzepatide) NCT04184622 |
Phase 3 RCT; n=2,539 adults with obesity or overweight-related comorbidities | Mean body weight reductions of 16.0% to 22.5% (dose-dependent) at 72 weeks vs. 2.4% with placebo |
Growth Hormone-Releasing Peptides
Sermorelin is a growth hormone-releasing hormone (GHRH) analogue that has been studied for its role in stimulating the body’s own production of growth hormone. Unlike directly administering growth hormone, sermorelin works further upstream in the signaling pathway. Celia offers sermorelin as a compounded prescription formulation.
Neuropeptides
Oxytocin is a neuropeptide produced in the hypothalamus that has been studied in relation to social bonding, stress response, and certain aspects of reproductive physiology. Celia offers oxytocin nasal spray as a compounded prescription formulation.
Metabolic Support Compounds
Some provider-guided programs also pair peptide therapies with adjunct compounds, such as metformin, long studied for its role in insulin sensitization, as part of a broader metabolic health approach rather than standalone peptide therapy.
Peptides in Skincare and Cosmetic Use
Not all peptides used in a medical context are therapeutic in the prescription sense. Cosmetic peptides are typically applied topically and have been studied for their potential role in skin appearance and barrier support, rather than for treating an underlying medical condition. These formulations are generally available without a prescription and are regulated differently from compounded or FDA-approved prescription peptide medications. Celia offers an eye cream and a night cream formulated with peptide ingredients as part of its topical skincare line, distinct from its prescription peptide programs.
Pros and Cons of Peptides
As with any area of medicine, there are both potential benefits and limitations associated with peptide-based approaches. It’s worth weighing both sides rather than viewing peptides as a uniformly positive or negative category.
Potential benefits that research has explored include:
- Targeted mechanisms of action, since peptides often interact with specific receptors rather than having broad, non-specific effects
- A growing body of clinical trial data for certain peptide classes, particularly for GLP-1 and dual-agonist medications
- Multiple formulation options (injectable, oral tablet, nasal spray) depending on the specific peptide and clinical goal
Limitations and open questions include:
- Many peptides, particularly outside the GLP-1 class, have less robust long-term human trial data compared to traditional small-molecule drugs
- Compounded peptide formulations are not independently FDA-approved, meaning they have not undergone the same large-scale safety and efficacy review as approved drugs
- Individual response varies significantly, and what research shows at a population level doesn’t predict any one person’s outcome
- Peptide stability and absorption can vary by route of administration, which is part of why formulation and dosing should be determined by a licensed provider
Does Peptide Therapy Have Side Effects?
Available evidence has evaluated the safety profiles of several well-studied peptides, and like any medication, they are associated with potential side effects. For GLP-1 and dual-agonist peptides, clinical trials have most commonly reported gastrointestinal effects such as nausea, diarrhea, and constipation, particularly during dose escalation.
In the STEP 1 trial, gastrointestinal disorders were reported in 74.2% of participants receiving semaglutide, compared with 47.9% of those receiving placebo, and 7.0% of the semaglutide group discontinued treatment due to adverse events, compared with 3.1% in the placebo group. Side effect profiles can differ meaningfully depending on the specific peptide, its mechanism, and how it is administered.
It is important to distinguish between FDA-approved peptide drugs, which carry detailed, trial-derived safety and side effect information on their labeling, and compounded peptide formulations. Compounded medications are prescription compounds dispensed by licensed 503A pharmacies. They are not FDA-approved drugs and have not been reviewed by the FDA for safety, efficacy, or quality in the way approved drugs have. This is one of several reasons why compounded peptide therapy should only be pursued after an individualized evaluation by a licensed healthcare provider, who can review personal health history, current medications, and potential interactions.
What to Understand Before Exploring Peptide Therapy
Before considering any peptide-based program, a few things are worth understanding:
- A prescription and clinical evaluation are required. Peptide medications, whether FDA-approved or compounded, are prescription-only and should be initiated only after a licensed provider has reviewed your health history.
- Not all peptides are equally studied. Some, like semaglutide and tirzepatide, have extensive Phase 3 trial data; others have a smaller, more preliminary evidence base.
- Compounded means different oversight, not no oversight. 503A pharmacies operate under state pharmacy board regulation and federal compounding standards, but their products are not reviewed and approved by the FDA the way manufactured drugs are.
- Individual results vary. Clinical trial averages describe a study population, not a guarantee for any one person.
| Curious Whether Peptide Therapy Fits Your Goals?
A licensed provider can review your health history and help determine which options, if any, may be appropriate for you. |
Frequently Asked Questions
Is there a downside to taking peptides?
Yes. Potential downsides include side effects that vary by peptide type, a comparatively limited long-term human safety record for many peptides outside the GLP-1 class, and the fact that compounded peptide formulations are not independently reviewed by the FDA for safety, efficacy, or quality. Cost and the need for ongoing provider supervision are also practical considerations. A licensed healthcare provider can help weigh these factors against your specific health history before starting any peptide-based program.
Is Ozempic considered a peptide?
Yes. Ozempic is a brand name for semaglutide, a GLP-1 receptor agonist, which is a peptide. It is an FDA-approved product manufactured by its original drug maker. Compounded semaglutide, such as the formulations Celia offers, contains the same active ingredient but is a distinct product that has not independently undergone the same FDA review for safety, efficacy, or quality.
Are peptides like steroids?
No, not in the way the term is typically used. Steroid hormones, including anabolic steroids and corticosteroids, are lipid-based molecules built from a cholesterol backbone. Peptides are chains of amino acids. They are structurally different classes of molecules that generally interact with different receptors in the body. Testosterone, for example, is a steroid, while growth hormone-releasing hormone is a peptide.
Can peptides be purchased without a prescription?
It depends on the peptide. Cosmetic peptides used in topical skincare are generally available without a prescription. Peptide medications used for therapeutic purposes, whether FDA-approved or compounded, are prescription-only and require evaluation by a licensed healthcare provider before they can be dispensed.
How long does it take to see results from peptide therapy?
Timelines vary by peptide, dose, and the individual, and no single timeframe applies to everyone. In the trials referenced above, researchers measured outcomes over fixed study periods, 68 weeks for STEP 1 and 72 weeks for SURMOUNT-1, rather than at a single point in time. A licensed provider can help set realistic expectations based on the specific peptide and program.
Can peptides interact with other medications?
Potentially, yes. As with any medication, interactions depend on the specific peptide, dose, and what else a person is taking. This is one of the reasons a licensed healthcare provider reviews current medications and health history before prescribing any peptide-based treatment, and why peptide therapy should not be started or adjusted without that evaluation.
