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Peptide Therapy: What It Is & How It Works

Peptide therapy has gone from niche biohacker territory to mainstream medicine in the span of a few years.

Peptide therapy has gone from niche biohacker territory to mainstream medicine in the span of a few years. The catalyst was GLP-1 drugs --- semaglutide and tirzepatide --- which turned peptide medications into household names. But the broader category of peptide therapy extends well beyond weight loss, encompassing FDA-approved treatments for diabetes, cancer, osteoporosis, rare genetic conditions, and more.

At the same time, a parallel world of off-label and experimental peptide use has grown through wellness clinics, compounding pharmacies, and online communities. Sorting the evidence-based from the speculative --- and knowing how to find a legitimate provider --- matters enormously for anyone considering peptide therapy.

This guide explains what peptide therapy actually is, how it differs from conventional drugs, what the evidence supports, what it costs, and how to navigate the field safely.

Table of Contents

What Is Peptide Therapy?

Peptide therapy is the use of peptides --- short chains of amino acids, typically between 2 and 50 --- to treat medical conditions or influence biological processes. Your body already produces hundreds of peptide hormones, neurotransmitters, and signaling molecules. Peptide therapy either replaces deficient natural peptides, supplements their activity, or uses synthetic analogs designed to be more stable, potent, or targeted than the originals.

The concept isn't new. Insulin therapy has been around since 1922. Synthetic oxytocin (Pitocin) has been inducing labor for decades. What changed is scale: the number of FDA-approved peptide drugs has roughly doubled since 2010, and the global peptide therapeutics market is projected to reach $49.68 billion in 2026.

At its core, peptide therapy exploits a simple biological principle. Peptides are the body's own signaling molecules. Instead of introducing a foreign chemical that forces a change (the way many traditional drugs work), peptide therapy aims to work with existing biological pathways --- amplifying, suppressing, or restoring signals the body already uses.

How Peptides Differ From Conventional Drugs

Understanding where peptides sit in the pharmaceutical spectrum helps explain their advantages and limitations.

Size

Small-molecule drugs (aspirin, metformin, statins) typically weigh under 500 daltons. Monoclonal antibodies weigh around 150,000 daltons. Peptide drugs sit in between, usually 500 to 5,000 daltons. This "middle space" gives them some properties of both worlds.

Specificity

Peptides tend to be highly specific for their targets. A GLP-1 agonist binds the GLP-1 receptor and not much else. This specificity generally translates to fewer off-target side effects compared to small molecules, which often interact with multiple receptors.

Metabolism

Most peptides are quickly broken down by enzymes (proteases) in the blood and gut. This is why natural GLP-1 has a half-life of about 2 minutes --- useless as a drug. Pharmaceutical companies solved this through chemical modifications: fatty acid acylation (semaglutide binds to albumin, extending its half-life to a week), PEGylation (attaching polyethylene glycol chains), and cyclization (making the peptide chain loop back on itself for protease resistance).

Delivery Challenges

The same enzymatic vulnerability that makes peptides short-lived also makes them hard to deliver orally. Most peptide drugs require injection --- typically subcutaneous (under the skin). Oral semaglutide (Rybelsus) was a breakthrough: it uses an absorption enhancer called SNAC to protect the peptide through the stomach. More oral peptide delivery technologies are in development.

Manufacturing

Peptides are made by solid-phase peptide synthesis (SPPS) or recombinant DNA technology. Both are well-established but more complex and expensive than small-molecule manufacturing. This contributes to the high price of many peptide drugs.

The Three Tiers of Peptide Therapy

Not all peptide therapy is created equal. The evidence, safety, and legal status vary dramatically depending on which tier a peptide falls into.

Tier 1: FDA-Approved Peptide Medications

These peptides have passed Phase 1, 2, and 3 clinical trials, demonstrated safety and efficacy in large human studies, and received formal FDA approval. They are manufactured under strict Good Manufacturing Practice (GMP) standards.

Examples:

  • Semaglutide (Ozempic/Wegovy) --- type 2 diabetes, obesity
  • Tirzepatide (Mounjaro/Zepbound) --- type 2 diabetes, obesity
  • Liraglutide (Victoza/Saxenda) --- type 2 diabetes, obesity
  • Tesamorelin (Egrifta) --- HIV-associated lipodystrophy
  • Teriparatide (Forteo) --- osteoporosis
  • Bremelanotide (Vyleesi) --- hypoactive sexual desire disorder

Evidence level: Strong. Multiple randomized controlled trials (RCTs) with thousands of participants.

Tier 2: Off-Label Prescribing of Approved Peptides and Compounded Peptides

Physicians can legally prescribe FDA-approved drugs for indications beyond their official label. They can also prescribe peptides prepared by compounding pharmacies when no commercially available product meets the patient's need.

Examples:

  • Sermorelin (was FDA-approved, now primarily compounded) --- growth hormone deficiency, anti-aging
  • CJC-1295 + ipamorelin (compounded) --- growth hormone optimization
  • PT-141 (bremelanotide is approved; PT-141 is sometimes compounded)
  • GHK-Cu (topical, compounded) --- skin rejuvenation, wound healing
  • Low-dose naltrexone combined with various peptides

Evidence level: Mixed. Some have reasonable supporting evidence; others rest primarily on animal studies and clinical observation. Manufacturing quality depends entirely on the compounding pharmacy.

Tier 3: Research Peptides (Unapproved)

These peptides have never been FDA-approved. They are sold as "for research use only" and are not legally marketed for human use, though many people obtain and use them.

Examples:

  • BPC-157 --- healing, gut repair (Category 2, banned from compounding)
  • TB-500 --- tissue repair, inflammation (Category 2, banned from compounding)
  • MK-677 --- growth hormone secretagogue (technically not a peptide; an oral GH secretagogue)
  • Epitalon --- telomerase activation
  • DSIP --- sleep regulation

Evidence level: Mostly preclinical (animal studies). Human data is scarce, often limited to case reports or small uncontrolled studies. A 2025 systematic review found that for BPC-157, 35 of 36 published studies were conducted entirely in animals. Manufacturing quality is unreliable --- FDA testing has found that up to 40% of online peptide products contain incorrect dosages or undeclared ingredients.

How Peptide Therapy Works in the Body

Peptide drugs work through the same receptor-mediated signaling pathways that natural peptide hormones use. Here's the general mechanism, followed by specific examples.

The General Pathway

  1. Administration: The peptide enters the bloodstream (via injection, oral absorption, or nasal spray)
  2. Binding: The peptide binds to specific receptors on target cell surfaces
  3. Signal transduction: Receptor binding activates intracellular signaling cascades, often through G proteins and second messengers like cAMP
  4. Biological effect: The cascade triggers the desired physiological response --- insulin release, appetite suppression, bone growth, hormone secretion, etc.
  5. Termination: The peptide is broken down by proteases or cleared by the kidneys, ending the signal

For a deeper explanation of these molecular mechanisms, see our guide on how peptides work.

Specific Mechanism Examples

GLP-1 agonists (semaglutide, tirzepatide): Bind GLP-1 receptors on pancreatic beta cells, stimulating glucose-dependent insulin release. They also bind GLP-1 receptors in the hypothalamus to suppress appetite and in the stomach to slow gastric emptying. The net effect: lower blood sugar, reduced hunger, weight loss. See our GLP-1 mechanism guide for a full breakdown.

GHRH analogs (sermorelin, CJC-1295): Bind GHRH receptors on pituitary somatotroph cells, stimulating growth hormone release in a pulsatile, physiological pattern. Unlike direct GH injection, they work through the body's own feedback loops.

Growth hormone secretagogues (ipamorelin): Bind ghrelin receptors (GHS-R) on pituitary cells to trigger GH release through a separate pathway from GHRH. Combining a GHRH analog with a secretagogue creates a synergistic effect.

Melanocortin agonists (bremelanotide/PT-141): Activate MC3R and MC4R receptors in the hypothalamus, affecting sexual arousal pathways. Unlike PDE5 inhibitors (Viagra, Cialis) that work on blood flow mechanics, bremelanotide works through central nervous system desire pathways.

Common Peptide Therapy Protocols

Protocols vary by peptide, condition, and prescribing physician. Here are typical structures for the most common peptide therapies.

GLP-1 Agonist Protocols (Tier 1)

Semaglutide (Ozempic/Wegovy):

  • Start at 0.25 mg once weekly (subcutaneous injection) for 4 weeks
  • Increase to 0.5 mg weekly for 4 weeks
  • Continue escalating every 4 weeks through 1.0 mg, 1.7 mg, to the target dose of 2.4 mg weekly
  • Slow titration minimizes GI side effects (nausea, which affects 20-44% of patients at higher doses)
  • Treatment is generally ongoing; weight regain is common when stopped

Growth Hormone Optimization Protocols (Tier 2)

CJC-1295/Ipamorelin combination (compounded):

  • Typical dosing: 100-300 mcg of each peptide
  • Injected subcutaneously 2-5 times per week
  • Usually administered before bed (to align with natural GH pulsatility)
  • Cycling: often prescribed in cycles of 3--6 months on, 1--2 months off
  • Lab monitoring: IGF-1 levels checked every 6--12 weeks

For details on this protocol, see our CJC-1295/ipamorelin stacking guide.

Healing Peptide Protocols (Tier 3 --- Experimental)

BPC-157 (research use only, banned from compounding):

  • Historically compounded at 200-500 mcg per injection
  • Injected subcutaneously near the injury site or systemically, 1-2 times daily
  • Typical course: 4-8 weeks
  • No standardized protocol exists because no clinical trials have established dosing

These protocols carry more uncertainty. Without human dose-response studies, all dosing recommendations come from extrapolation of animal data, clinical experience from prescribers, and anecdotal reports.

Routes of Administration

RoutePeptides Used This WayAdvantagesDisadvantages
Subcutaneous injectionSemaglutide, tirzepatide, CJC-1295, ipamorelin, BPC-157, most peptidesHigh bioavailability, self-administered at home, consistent absorptionRequires injection technique, needle anxiety, injection site reactions
OralSemaglutide (Rybelsus), linaclotide, trofinetideNo needles, patient convenienceLow bioavailability for most peptides; requires absorption enhancers; must be taken on empty stomach
IntranasalDesmopressin, oxytocin (research), some nootropic peptidesBypasses GI degradation, may access CNS directlyVariable absorption, nasal irritation, dosing inconsistency
TopicalGHK-Cu, cosmetic peptides (Matrixyl, Argireline)Non-invasive, localized effectLimited to skin; systemic absorption minimal
IntrathecalZiconotide (Prialt)Direct CNS delivery, potent pain reliefRequires surgical pump implant, specialist management
IntramuscularSome peptide vaccines, depot formulationsLonger absorption time, depot effectMore painful than subcutaneous

The vast majority of peptide therapy involves subcutaneous injection. For a step-by-step technique guide, see our peptide injection guide.

The Evidence Base: What the Science Actually Shows

Honest assessment of the evidence matters. Here's where the major categories stand.

Strong Evidence (Large RCTs, FDA Approval)

  • GLP-1 agonists for diabetes and obesity: The STEP trials for semaglutide enrolled over 4,500 participants; SURMOUNT trials for tirzepatide included over 5,000. Both showed 15--22% body weight reduction with sustained metabolic improvements. Cardiovascular outcome data (SELECT trial) showed 20% reduction in major adverse cardiac events with semaglutide.

  • GnRH analogs for cancer: Leuprolide, goserelin, and degarelix have decades of evidence for hormone-sensitive cancers. Established standard-of-care.

  • Teriparatide for osteoporosis: Multiple RCTs demonstrate increased bone mineral density and reduced fracture risk.

  • Insulin for diabetes: Over a century of clinical use and thousands of studies.

Moderate Evidence (Smaller Trials, Consistent Results)

  • Tesamorelin for lipodystrophy: Two Phase 3 trials showed significant reduction in visceral adipose tissue.

  • Growth hormone-releasing peptides (sermorelin, GHRH analogs): Sermorelin had FDA approval before being voluntarily withdrawn (manufacturing issues, not safety). Clinical data from its approval period showed effective GH stimulation. Newer GHRH analogs have fewer published trials.

  • Thymosin alpha-1 for immune modulation: Approved outside the US (marketed as Zadaxin in Asia). Multiple clinical trials for hepatitis, immunodeficiency, and as a vaccine adjuvant, though many were small.

Limited Evidence (Mostly Preclinical)

  • BPC-157: A 2024 systematic review found 36 published studies, with 35 conducted entirely in animals. The single human study was a retrospective case series of 12 people with subjective knee pain and no control group. Animal data is consistently positive across dozens of injury models, but the translation to humans is unproven.

  • TB-500: Similar story. Animal studies show wound healing and anti-inflammatory effects. No published human RCTs.

  • Epitalon: Animal studies (primarily from the Khavinson group in Russia) suggest telomerase activation. No controlled human trials published in peer-reviewed Western journals.

  • Selank and Semax: Russian-developed nootropic peptides with some clinical data from Russian trials, but most studies haven't been replicated outside of Russia and aren't indexed in Western databases.

The pattern to watch for: Many peptides in Tiers 2 and 3 have robust animal data and plausible mechanisms of action, but the gap between animal studies and proven human benefit is large. Dosing, bioavailability, long-term safety, and drug interactions remain unknown for most of them.

Finding a Legitimate Provider

If you're considering peptide therapy, the provider you choose matters as much as the peptide itself.

What to Look For

  • Licensed physician (MD or DO) with training in endocrinology, functional medicine, or anti-aging medicine
  • Thorough initial workup including blood panels (hormone levels, metabolic markers, liver/kidney function) before starting any peptide
  • Ongoing monitoring with regular lab work and follow-up appointments
  • Prescriptions from licensed compounding pharmacies that follow USP 797/800 standards
  • Willingness to discuss evidence honestly --- including what a peptide can't do and where the data is thin
  • Transparent pricing without pressure to commit to long-term packages upfront

Red Flags

  • Clinics that sell peptides directly (rather than writing prescriptions to independent pharmacies)
  • No lab work required before or during treatment
  • Promises of dramatic results with no mention of limitations or side effects
  • "Research chemical" peptides sold without a prescription
  • Providers who aren't physicians (non-licensed "peptide coaches")
  • High-pressure sales tactics or mandatory multi-month commitments

For more guidance, see our detailed guide on how to choose a peptide therapy clinic and our article on talking to your doctor about peptides.

What Peptide Therapy Costs

Costs vary enormously depending on the peptide, whether it's FDA-approved or compounded, and the provider.

FDA-Approved Peptide Drugs

DrugMonthly Cost (Without Insurance)Insurance Coverage
Semaglutide (Ozempic)$900--$1,300Often covered for diabetes; variable for weight loss
Tirzepatide (Mounjaro)$1,000--$1,200Covered for diabetes; Zepbound coverage variable
Liraglutide (Saxenda)$1,200--$1,500Sometimes covered for obesity with documentation
Tesamorelin (Egrifta)$1,500--$2,500Covered for HIV lipodystrophy
Teriparatide (Forteo)$3,000--$4,000Usually covered for osteoporosis with prior authorization

Compounded Peptide Therapy

Peptide/ProtocolMonthly Cost (Typical)Notes
Sermorelin$150--$400Varies by pharmacy and dose
CJC-1295/Ipamorelin$200--$500Combination pricing
PT-141 (as-needed)$100--$300Per-dose pricing common
GHK-Cu (topical)$50--$150Compounded creams and serums
Full clinic protocol (peptide + monitoring + consults)$400--$2,000Includes provider visits and lab work

What Insurance Covers

Most compounded peptide therapy is not covered by insurance. FDA-approved peptides are covered when prescribed for their approved indications, though prior authorization is often required. HSA/FSA accounts can typically be used for medically necessary peptide prescriptions.

For a comprehensive breakdown, see our peptide therapy insurance coverage guide.

Safety, Side Effects, and Risks

Common Side Effects (Vary by Peptide)

GLP-1 agonists: Nausea (20-44% of patients, usually transient), vomiting, diarrhea, constipation, injection site reactions. Less common: pancreatitis, gallbladder disease, thyroid C-cell concerns (preclinical signal, no confirmed human risk).

Growth hormone secretagogues: Water retention, increased hunger (especially GHRP-6), tingling/numbness, transient cortisol or prolactin elevation.

General injection-related: Injection site redness, swelling, pain, bruising. Proper technique and site rotation minimize these.

Serious Risks to Consider

Purity and contamination. FDA testing of peptides from online sources and some compounding pharmacies revealed that up to 40% contained incorrect dosages or undeclared ingredients. Using impure peptides introduces unpredictable risks.

Unknown long-term effects. For Tier 2 and 3 peptides, long-term safety data simply doesn't exist. This is particularly concerning for peptides used chronically (months to years).

Drug interactions. Peptide-drug interactions are poorly studied. GLP-1 agonists can slow absorption of oral medications due to delayed gastric emptying. Growth hormone secretagogues may interact with diabetes medications. Always inform your prescriber of all medications you take.

Contraindications. Specific peptides carry specific contraindications. GLP-1 agonists are contraindicated in personal or family history of medullary thyroid carcinoma. GH-stimulating peptides should be avoided in active cancer. Pregnancy and breastfeeding are contraindications for most peptide therapies.

The Regulatory Environment in 2026

The peptide regulatory environment has shifted dramatically since 2023.

Key Developments

FDA compounding restrictions. The FDA has placed BPC-157 and TB-500 on its Category 2 list (substances with safety concerns), banning them from pharmacy compounding for human use. In 2025, the FDA expanded Import Alert 66-78 to include 12 additional peptides, targeting imports of research-grade peptides intended for human use.

GLP-1 compounding battles. As semaglutide's drug shortage ended, compounded semaglutide's legal status became contested. The FDA moved to restrict compounding, while compounding pharmacies and some patient advocacy groups pushed back. This remains in flux as of early 2026. See our detailed coverage of the GLP-1 compounding situation.

DEA interest. Certain growth hormone secretagogues have come under DEA scrutiny due to misuse in sports. Reclassification as controlled substances has been discussed but not yet enacted for most peptides.

Telehealth prescribing. Telehealth peptide clinics boomed during 2023--2025. Regulatory bodies are now scrutinizing these operations, particularly those that prescribe without adequate medical evaluation. For guidance on telehealth peptide prescriptions, see our legal framework guide.

What This Means for Patients

The practical takeaway: the line between legal and illegal peptide use keeps moving. FDA-approved medications prescribed by licensed physicians remain fully legal. Compounded peptides prescribed by physicians exist in a narrowing gray zone. "Research use only" peptides purchased directly by consumers occupy increasingly risky legal territory.

FAQ

Is peptide therapy the same as hormone replacement therapy (HRT)?

Not exactly, though there's overlap. Some peptide therapies (like GHRH analogs) stimulate your own hormone production, while HRT replaces hormones directly (testosterone injections, estrogen patches). Many clinicians combine both approaches. For a detailed comparison, see our peptide therapy vs. HRT guide.

How long does it take for peptide therapy to work?

It depends on the peptide. GLP-1 agonists typically produce noticeable appetite changes within the first week, with significant weight loss over 3--6 months. Growth hormone peptides may take 4--12 weeks for noticeable effects on body composition and energy. Healing peptides (BPC-157, TB-500) are reported anecdotally to show effects within 2--4 weeks, but no clinical data confirms this timeline.

Can I take peptides without a doctor?

Legally, FDA-approved peptides require prescriptions. "Research use only" peptides exist in a legal gray area --- they're not approved for human use. From a safety perspective, medical supervision is strongly recommended for any peptide therapy. Lab monitoring, dosage adjustment, and awareness of contraindications all require medical expertise.

Do I need to cycle peptide therapy?

Some peptides are used continuously (GLP-1 agonists for chronic conditions). Others are typically cycled (growth hormone secretagogues: 3--6 months on, 1--2 months off) to prevent receptor desensitization. There's no universal rule --- cycling protocols are peptide-specific and often based on clinical experience rather than hard data. For guidance, see our peptide cycling guide.

What happens when I stop peptide therapy?

It depends on the peptide and condition. Stopping GLP-1 agonists typically leads to appetite return and weight regain (the STEP 1 extension trial showed patients regained roughly two-thirds of lost weight within a year of stopping). Stopping growth hormone peptides returns GH levels to pre-treatment baseline. Whether benefits from healing peptides persist after stopping is unknown.

Are peptide injections painful?

Most peptide injections use small-gauge needles (27--31 gauge, insulin syringe size) for subcutaneous injection into belly fat or thigh. Most patients describe it as a brief pinch. Injection site reactions (redness, itching) occur in 5--15% of patients but are usually mild and transient.

Is peptide therapy safe during pregnancy?

Most peptide therapies are contraindicated during pregnancy and breastfeeding due to insufficient safety data. GLP-1 agonists are specifically contraindicated. Growth hormone peptides, healing peptides, and most others should be discontinued before attempting conception. Always discuss reproductive plans with your prescriber.

The Bottom Line

Peptide therapy spans a wide spectrum --- from century-old insulin injections to experimental research compounds purchased online. The key to navigating it safely is understanding which tier a peptide falls into and calibrating your expectations accordingly.

For FDA-approved peptide medications: The evidence is strong, manufacturing quality is guaranteed, and insurance may cover the cost. If you have diabetes, obesity, osteoporosis, or another condition with an approved peptide treatment, these are legitimate, well-studied options. Start with your physician.

For compounded and off-label peptides: The evidence is thinner, quality control depends on the pharmacy, and costs come out of pocket. A qualified physician who monitors your labs and knows the literature can help manage the risk. But understand that you're working with less data than you would with an FDA-approved drug.

For research-only peptides: The evidence base is mostly animal studies, purity is not guaranteed, and the legal ground is shifting. Proceed with caution and informed consent if you choose this path --- and ideally with physician oversight.

The peptide therapy field is evolving rapidly. New FDA approvals, new clinical trial data, and new regulatory decisions are announced regularly. Stay informed through reliable sources, work with qualified providers, and be appropriately skeptical of claims that outpace the evidence.

For more, explore our guides on choosing a peptide therapy clinic, understanding peptide side effects, and the complete list of FDA-approved peptide drugs.

References

  1. Therapeutic Peptides: Recent Advances in Discovery, Synthesis, and Clinical Translation. PMC. 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12154100/

  2. Advance in peptide-based drug development: delivery platforms, therapeutics and vaccines. Signal Transduction and Targeted Therapy. 2024. https://www.nature.com/articles/s41392-024-02107-5

  3. Peptide Therapy Trends 2026: What Clinics Must Know. OptiMantra. https://www.optimantra.com/blog/peptide-therapy-trends-to-watch-in-2025-what-clinics-need-to-know

  4. Injectable peptide therapy went mainstream in 2025, priming consumers for the next big wellness wave. Glossy. 2025. https://www.glossy.co/beauty/injectable-peptide-therapy-went-mainstream-in-2025-priming-consumers-for-the-next-big-wave-in-wellness/

  5. Peptide Therapies in 2025: What's Legal, What's Experimental, and What the Science Says. Empire On-Demand. https://empireondemand.com/blogs/posts/peptide-therapies-in-2025-whats-legal-whats-experimental-and-what-the-science-says

  6. 2024 FDA TIDES (Peptides and Oligonucleotides) Harvest. Pharmaceuticals. 2025;18(3):291. https://pmc.ncbi.nlm.nih.gov/articles/PMC11945313/

  7. Deep Dive: Regulatory Status of Popular Compounded Peptides. Holt Law. https://djholtlaw.com/deep-dive-regulatory-status-of-popular-compounded-peptides/

  8. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine. 2021;384:989-1002. https://pubmed.ncbi.nlm.nih.gov/33567185/

  9. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387:205-216. https://pubmed.ncbi.nlm.nih.gov/35658024/

  10. Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). New England Journal of Medicine. 2023;389:2221-2232. https://pubmed.ncbi.nlm.nih.gov/37952131/