Beginner’s Guide to Peptide Therapy

Peptides are a growing subject of curiosity for many people. Advertisements and online discussions suggest that these medicines may be a miracle solution for achieving myriad health outcomes, including but not limited to weight loss, muscle growth, longevity, and overall well-being. Recently, the peptide space has seen a significant uptick in drug discovery, clinical research, and therapeutic application.25 Even so, they remain a mystery to a lot of prospective patients, who aren’t exactly sure what peptides are or how they work.

It’s not their fault. Peptides are a complex subject with strange drug names, shared and sometimes contradictory potential effects, and confusing regulatory statuses. That’s why we’ve written this guide and structured it as we have. Where applicable, as we discuss each aspect of different peptide therapies, we start with a high-altitude view and then zoom in on the caveats and exceptions that make them unique. That way, you get both a broad sense of how peptides can work and a specific sense of which ones might work for you.

In the end, we trust you’ll have all the information you need to make the best-informed decision about your own peptide therapy, should you pursue it.

Over the past two decades, Innerbody Research has helped tens of millions of readers make more informed decisions about staying healthy and living healthier lifestyles.

Our team has been exploring the peptide space for years. For every hour we’ve put into writing about peptides, we’ve devoted two or three hours to research. All told, our total clock time on the subject exceeds 1,000 hours — a conservative estimate from which we pull further and further away with each week. Along the way, we’ve gained invaluable insights from medical providers who prescribe peptides, as well as from people who use them.

Additionally, like all health-related content on this website, this guide was thoroughly vetted by one or more members of our Medical Review Board for accuracy and will continue to be monitored for updates by our editorial team.

Peptides occur naturally in the body (endogenous) but can also be administered externally (exogenous).

The basics that underlie all peptides, endogenous and exogenous alike, are these:

• Peptides are strings of amino acids.
• Amino acids are molecules that combine to form protein molecules.
• Proteins are essential for a diverse array of bodily functions, including but not limited to immune function, muscle contraction, metabolism, physical growth, physical structure, blood oxygenation, and sexual arousal.1

The human body needs an adequate supply of 20 amino acids to function properly,2 but those 20 amino acids can combine in thousands of unique sequences to form different peptides with distinct biological functions. By supplementing your endogenous supply of peptides with exogenous sources, you provide your body with more of the resources it needs to carry out specific functions.

Therapeutic peptides

Those exogenous sources, when used to treat health conditions, are called therapeutic peptides. Given the varied roles that peptides assume in the human body, you can imagine that therapeutic peptides have a vast array of potential applications in human health. By way of example, consider this table of common therapeutic peptides and their primary health outcomes:

In many cases, therapeutic peptide prescriptions are given off-label (i.e., to treat health conditions other than what a peptide is approved for).

Take tesamorelin, for example. As an analog of endogenous growth hormone-releasing hormone (GHRH), tesamorelin boasts a metabolism-stimulating activity that has led to its being approved as a treatment for lipodystrophy, or abnormal adipose fat accumulation associated with antiretroviral therapy for HIV.3 But this same activity can help non-HIV individuals shed abdominal fat of their own, while the peptide’s GHRH properties make it a suitable therapy for people looking to increase their lean mass. Therefore, it isn’t uncommon to see tesamorelin given as an off-label prescription for weight loss or muscle growth.

Routes of administration

With regard to routes of administration, therapeutic peptides are often injectables, administered subcutaneously by needle. That’s because peptides degrade easily in the digestive tract and tend to be too large molecularly to permeate the skin or intestinal lining,5 yielding a bioavailability as low as 1-2%.6 But there are some peptides that have a small enough molecular size that they easily transfer into the bloodstream as either an oral or topical supplement — good examples being collagen, with an oral bioavailability as high as 63%,7 and GHK-Cu (copper peptides), which can pass through the skin in therapeutically effective amounts per a 2010 study.8

Preparation and storage of injectable peptides

An injectable peptide normally comes in powder form. Before you can use it, you must reconstitute it into a solution. Likely, your peptide prescription will also come with everything you need to do just that — bacteriostatic water and needle syringes.

Generally, the reconstitution process entails drawing a measure of bacteriostatic water into a syringe and then introducing that water to the peptide powder. Your prescriber’s instructions should specify how much water to use and how to dissolve the powder. However much water you’re supposed to use, avoid shaking the solution, as it can degrade the peptide.

A shipment of peptide powder, once reconstituted, should last a month when stored appropriately. The ideal storage temperature is around 4°C, or 39°F,9 so a refrigerator is the best place for it.

While peptides can potentially serve myriad health goals, we can broadly organize the most commonly sought-after peptides into five categories based on their primary benefits. In the following sections, we discuss those categories and the peptides most often associated with them.

Weight loss peptides (GLP-1 RAs)

Originally developed as diabetes treatments, glucagon-like peptide 1 receptor agonists (GLP-1 RAs) exhibit mechanisms of action on metabolism and the pancreas that promote weight loss by:26

• Slowing digestion: A longer time to gastric emptying correlates not only with a decreased appetite but also with a milder glucose spike.27 28 A decreased appetite means less desire to consume excess calories, and a less severe spike indicates tighter regulation over a significant weight-gain factor.29
• Increasing feelings of fullness: When you do get hungry, a GLP-1 can help you reach satiety sooner than you normally would. Ideally, that leads to eating less food during mealtimes and, therefore, consuming fewer calories throughout the day.

Today, the most popular and widely used peptides for weight loss are tirzepatide and semaglutide, which you may know by the respective brand names Mounjaro and Ozempic. Both have a wealth of scientific support for their efficacy, but tirzepatide has a bit more magnitude behind it. In a 2021 study, for example, subjects who received tirzepatide lost around 4-12 more pounds than their semaglutide counterparts.30 But semaglutide is still a terrific option for fast weight loss, and it’s more easily accessible through reputable telehealth platforms such as Hims, Hers, Ro, and Strut.

Body recomposition

Body recomposition refers to the process of gaining muscle and shedding fat. In our categorization, it’s the muscle growth factor that separates body recomposition peptides from GLP-1 RAs.

Many body recomposition peptides are growth hormone secretagogues, or substances that stimulate the body’s production of growth hormone, which itself promotes physical growth and helps regulate body fat composition through another hormone called insulin-like growth factor-1.31 32 Some of the more commonly used growth hormone secretagogue peptides are CJC-1295, ipamorelin, sermorelin, and tesamorelin. (Tesamorelin is also prescribed to treat HIV-associated lipodystrophy, or excess abdominal fat accumulation resulting from antiretroviral therapy. That is, in fact, the application for which it’s FDA-approved.)

Besides growth hormone secretagogues, there are uncategorized peptides that many physically active people use to increase their muscle mass, such as BPC-157 and thymosin beta-4 (TB4). These two peptides are often used together for their synergistic potential to stimulate muscle gain while speeding up recovery.

General wellness

Peptides for general wellness constitute the broadest category, as wellness refers to several target health outcomes: longevity, immune health, and quality of life (the last of these itself being a pretty broad subcategory). Often, the peptides under this category support all three outcomes. Examples of such peptides include:

• MOTS-c: MOTS-c is a naturally occurring protein hormone that may improve metabolic function,33 reduce inflammation,34 and improve bone health,35 among other things.
• Epitalon: Consisting of four amino acids, epitalon can help preserve the lengths of telomeres (the caps on the ends of chromosomes) and regulate melatonin. In doing so, it may stave off age-related diseases associated with telomere shortening,36 strengthen the immune system,37 and improve sleep health.38
• Delta sleep-inducing peptide (DSIP): As its name suggests, DSIP helps with sleep. It may also attenuate stress and have applications as an anticonvulsant, antidepressant, and neuroprotective agent.39
• Thymosin alpha-1: Thymosin alpha-1 may offer numerous benefits related to immune function, including but not limited to treating hepatitis B, treating infections, improving vaccine efficacy, and reducing the toxicity of chemotherapy.40
• GHK-Cu: GHK-Cu is a complex of the peptide GHK and copper. It has quality-of-life applications related to skin health, as research supports its ability to tighten loose skin, improve skin firmness, reduce photodamage, promote wound healing, and more.41
• Insulin: Insulin is a quality-of-life treatment for managing blood sugar. It’s helpful for people with type 2 diabetes and necessary for those with type 1 diabetes.42

Cognitive enhancement

Cognitive enhancement peptides are similar to nootropics in that they can improve focus, memory, and mental clarity, as well as associated factors like anxiety and mood. Two promising synthetic peptides in this category are Selank and Semax. With the former, studies have shown that it can produce a stable and sustained influence on learning and memory,43 while the latter may be able to support the differentiation, maturation, and survival of neurons in the brain.44

Another potential cognitive enhancement peptide is Pinealon, which can improve learning and memory by modulating gene expression and neurotransmitter activity. In rodents at least, Pinealon administration correlated with an improved ability to negotiate a maze,45 suggesting that the subjects could acquire and retain information more effectively.

Sexual function

Peptides for sexual function are alternatives or additions to more ordinary prescription treatments such as sildenafil and tadalafil. One such peptide, called **PT-141 (a.k.a. bremelanotide), has been described as a “promising way to treat [hypoactive sexual desire disorder],”46 a condition characterized by a chronic lack of sexual desire.47 PT-141 is available as a women-only prescription under the brand name Vyleesi, clinical trials for which have shown the drug to both improve sexual desire and decrease feelings of being bothered by a low sexual desire.48

PT-141 has also been tested in men, as in a 2005 study that coadministered the peptide with sildenafil to subjects with ED who either had not responded to or could not tolerate single-therapy treatment. Among this cohort, coadministration was deemed to be a “viable therapy.”49

A separate peptide solution, for both men and women, is oxytocin, which may have some role in stimulating sexual attraction.50 But more research is needed, as some research has found oxytocin to be ineffective at improving sexual behavior.51

Besides their specific use applications, we can broadly classify therapeutic peptides into three categories based on how they’re produced for the market:

• Bioactive peptides
• Synthetic peptides
• Recombinant peptides

Their differences lie not in the efficacy of the resulting peptide therapy but in feasibility and cost-effectiveness. That is, from a production perspective, some peptide varieties lend themselves more to one production method than the others.

Bioactive peptides

Bioactive substances are found in animal and plant matter, so bioactive peptides might also be categorized as natural peptides.10

Bioactive peptides can be consumed via dietary sources, including but not limited to eggs, soy, legumes, meat (including seafood), and dairy.11 Or else they can be isolated, extracted, and processed into oral or even topical supplements. Two common production techniques for bioactive peptides are enzymatic hydrolysis and microbial fermentation, which are both ways to break proteins down into smaller peptides or individual amino acids.12

The realm of bioactive peptides is somewhat limited because, remember, peptides can easily break down in the digestive tract, and many are too molecularly large to permeate the skin or intestinal lining.5 But there are several peptide varieties that are readily bioavailable by oral or transcutaneous administration, such as collagen and GHK-Cu.

Synthetic peptides

Synthetic peptides are lab-derived, created by deliberately linking amino acids in sequences that mimic endogenous peptides. It’s by this method that you get some of the best-known pharmaceutical peptides, like semaglutide, tirzepatide, and tesamorelin.

If endogenous peptides are like OEM parts in the machinery of your body, then we can liken synthetic peptides to 3D prints: in terms of structure and function, they’re similar if not identical.

The drawback of synthetic peptides is that they’re largely limited to short chains of up to 50 amino acids, as longer peptides are more challenging from a large-scale-manufacturing perspective.13

Recombinant peptides

Recombinant peptides are those produced via recombinant DNA technology. In other words, scientists manipulate and isolate DNA segments to express the genes of specific peptides.14 Think of it as the Venn common ground between the bioactive and the synthetic, a biotechnological hybrid relying on both organic and laboratory processes. With recombinant technology, therapeutic peptide chains can more easily exceed 50 amino acids. Producing such peptides can be costlier, at least up front, but may be more efficient on larger scales.

In theory, pharmaceutical-grade therapeutic peptides are generally safe because peptides already occur in the human body. That includes synthetic peptides, which mimic their naturally occurring counterparts in form and function. For example, a normally functioning body already produces collagen and GHRH, so adding collagen peptides or a GHRH analog should only enhance naturally occurring biological processes. For most non-pregnant, non-breastfeeding people without specific allergies, adverse events are limited to mild and transient flu-like effects and (for injectables) injection site reactions.

But in practice, and especially with regard to synthetic and recombinant peptide forms, there are some serious safety concerns:

These are only the prominent issues associated with some of the better-known therapeutic peptides. When you more thoroughly explore the peptide pantheon, you’ll find that more obscure peptide treatments have been known to cause other life-threatening issues such as:19

• Heart toxicity (cesium chloride)
• Arrhythmias (cesium chloride, domperidone)
• Kidney injury (germanium sesquioxide)

Peptide legality is a complex issue. Some therapeutic peptides (e.g., collagen) are readily available over the counter. Some need a doctor’s prescription but are otherwise widely available (e.g., GLP-1 RAs like semaglutide and tirzepatide). But then there are others that, in the United States, currently drift in a state of legal limbo.

The complexities arise from Section 503A of the Federal Food, Drug, and Cosmetic Act, which relates to the necessary conditions for drug compounding.20 The rules concerning the compounding of therapeutic peptides state that they must come from accredited compounding pharmacies, and the compounded drug must either be compounded from an existing FDA-approved drug product or use drug products included on the FDA’s roster of compoundable substances, the 503A bulks list.21

But many therapeutic peptides don’t satisfy either of the 503A conditions. That includes several that we’ve highlighted in this guide:22

• BPC-157
• CJC-1295
• Epitalon
• GHK-Cu (as an injectable)
• Ipamorelin
• MOTS-c
• Selank
• Semax
• Thymosin alpha-1
• Thymosin beta-4

That doesn’t mean that you can’t get a prescription for those peptides; Section 503A allows for exemptions. With a valid prescription indicating that a compounded treatment is “necessary for the identified patient,” any of the above peptides could be made available.23 Just know that necessary is an operative word there. A doctor may prescribe you a peptide, but they must also document why you can’t use other, less legally restricted treatment options.

Most of the pharmaceutical-grade peptides available online are glucagon-like peptide-1 receptor agonists (GLP-1 RAs), which are primarily used for weight loss and diabetes management. Normally, your options are either semaglutide or tirzepatide, the two best-studied and widely used GLP-1 RAs. To date, we’ve identified nine reputable online platforms that sell one or both of these peptides:

Because GLP-1 RAs are prescription medications, each of the above platforms employs licensed medical professionals to conduct consultations with prospective patients. If you pass the consultation, you get approved for a prescription.

Notice, at the top of this section, we said pharmaceutical-grade peptides. Lesser-known peptides are also available online, but many are research-grade products not intended for human consumption. You can get them without a prescription, but unless you mean to conduct your own in vitro experiments, you should leave them alone. That’s because research-grade peptides aren’t subject to the same quality controls associated with their pharmaceutical-grade counterparts, and many come with purity levels as low as 60%.4 Thus, they have a greater potential to be toxic and cause the life-threatening adverse effects we discuss under “Therapeutic peptide safety.”

You can find pharmaceutical-grade versions of non-GLP-1 peptides online. You simply need to be more careful if you’re seeking a peptide therapy for something like muscle growth, immune function, longevity, or another health concern unrelated to weight loss. Read the product pages carefully, speak with a customer support representative when possible, and speak with a medical professional for their advice about patient-oriented peptide retailers online.

The 503A bulks list is a living document, continuously in flux. The restricted peptides we’ve listed may one day find their way onto the list, thereafter becoming widely available to prescribed patients. Meanwhile, new potential peptide drugs are being discovered,24 suggesting promising but as-yet-undetermined directions in the treatment of common health concerns. So, as developments and trends emerge, we’ll update this guide accordingly, keeping you current on the information you need to direct your own peptide therapy.