Peptides: Benefits, Side Effects, Safety, Usage

Peptides are versatile naturally occurring molecules that play a myriad of different functions within the human body and possess significant therapeutic potential.

Yet, it was not until the 1920s when the peptide hormone insulin was first isolated, and its use set the beginning of what is now called peptide therapy.

Currently, scientists can manufacture a wide variety of peptides, each with its unique potential benefits and medical applications.

For example, some peptides have been shown to boost collagen production and improve skin health, while others can facilitate weight loss in obesity, stimulate muscle growth in wasting disorders, speed up the healing of various tissues, and more!

Numerous peptides are already approved for human use and are widely prescribed for the treatment of medical conditions.

Patients should note that they can obtain safe and legal peptide therapy only after consultation with a qualified medical specialist. The use of unregulated peptides hides serious risks regarding the safety and effectiveness of the therapy.

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What are peptides?

Peptides are organic molecules composed of amino acids. These amino acids are connected through peptide bonds and form chains, similar to proteins.

Yet, peptides are much shorter, and their peptide chains usually comprise 2-50 amino acids. Most peptides have a linear configuration, but some can also have non-linear or cyclic structures.

It is the specific sequence and arrangement of these amino acids that dictate the unique characteristics and functions of the peptide. Some of these molecules are also bound to non-peptide entities, such as fatty acids, which further influence the peptide’s attributes.

In addition to the peptides that occur naturally in living organisms, these molecules can also be manufactured using a method called solid-phase peptide synthesis (SPPS), which involves amino-acid coupling reactions.

In simpler terms, this method entails building the peptide chain by sequentially adding amino acids in the correct order, beginning from the C-terminus.

Peptides are organic molecules usually comprised of 2-50 amino acids

These man-made peptides can be used for therapeutic purposes, as they usually mimic the function of naturally occurring molecules in the human body and activate various target receptors.

Currently, over 60 such peptide-based drugs have gained approval by various regulatory bodies throughout the world, such as the US Food and Drug Administration (FDA), and are legally available with a prescription for various indications.

Moreover, hundreds of other peptides are currently under active research. They are yet to be approved for human use, and therefore they can be legally used only in research settings.

Many peptides can also be purchased online under the pretense that they will be employed as reference materials for laboratory research.

In reality, the buyers often take the peptides for personal use, despite the fact that such forms of peptides lack regulation and are illegal for human use.

Due to the lack of regulation, such peptides may be counterfeit, contaminated, or expired, ultimately leading to a lack of effectiveness and potential health risks.

What do peptides do?

Peptides play multifaceted roles in human physiology, which has drawn considerable interest in medicine and research.

Some serve as messengers, facilitating communication between cells and organs, while others operate as hormones, regulating essential processes like appetite, growth, metabolic activity, and tissue regeneration.

Peptides offer a platform for designing novel drugs and treatment modalities because of their ability to engage with particular receptors and influence specific biological pathways. For example, peptides may work by mimicking the function of various hormones:

  • Mimetics of the incretin hormones – GLP-1 receptor agonists (semaglutide), GLP-1/GIP agonists (tirzepatide), etc.
  • Mimetics of the hunger hormone ghrelin – growth hormone secretagogues (GHS) such as ipamorelin, hexarelin, GHRP-2, GHRP-6, etc.
  • Growth hormone-releasing hormone (GHRH) analogs – sermorelin, tesamorelin, CJC 1295
  • Mimetics of the α melanocyte-stimulating hormone (α-MSH) – melanocortin receptor agonists such as Melanotan-1, Melanotan-2, PT-141
  • IGF-1 receptor agonists – IGF-1 LR3, IGF-1 DES, etc.


Peptides may also work by inhibiting enzymes or other signaling molecules (5-Amino-1MQ, Follistatin), acting as bioregulators of DNA expression (epithalon), regulating cellular motility (thymosin beta-4, TB-500), and many other mechanisms.

Many of these peptides include various modifications that differentiate them from their naturally-occurring counterparts. They can be modified via amino acid replacement, addition, and removal of peptide fragments or the addition of non-peptide structures that enhance their half-life, stability, effectiveness, and safety.

List of peptides and what they do

Here are some of the most notable therapeutic peptides approved for human use as well as some research peptides still under investigation:


Sermorelin (GRF 1-29) is a GHRH-mimetic that has held FDA approval for treating growth failure in children.

The peptide has also been tested in adults, more specifically in doses of 1-2 mg daily, and it has shown a potential for increasing growth hormone levels, improving body composition and enhancing collagen production.


Tesamorelin is a GHRH-mimetic that is approved for therapy in patients with HIV who also suffer from lipodystrophy.

The peptide has been tested in healthy but obese individuals, and 2 mg tesamorelin daily has led to a significant reduction of visceral obesity.


PT-141 is an analog to the α-MSH and works by activating the melanocortin receptors (MCRs), predominantly MC4R, which plays a role in sexual function, amongst other effects.

The peptide is currently approved for improving libido in premenopausal women with hypoactive sexual desire disorder (HSDD).

In addition, studies suggest that it works within 45 minutes when applied as a single dose of 1.75mg and increases libido in both men and women.


CJC-1295 is a tetrasubstituted version of sermorelin which is attached to a compound called Drug Affinity Complex (DAC), that extends its half-life from 30 minutes (mod GRF 1-29) to about a week.

A single dose of the peptide leads to increases in mean plasma growth hormone (GH) concentrations by 2- to 10-fold for over six days and in mean plasma IGF-I concentrations by 1.5- to 3-fold for about ten days.

Real benefits of peptides

As mentioned, peptides can have a wide range of benefits, which vary depending on the specific compound and its properties.

Main benefits of peptides for men and women

Currently, several therapeutic peptides are FDA-approved as effective and officially used for enhancing libido, improving weight loss, stimulating growth, etc.

Many have also been studied for their potential benefits related to tissue healing, skin health, muscle growth, wasting disorders, osteoporosis management, and more.

Here are some of the most notable potential and proven benefits of peptides:

Boosting weight loss

Peptides that belong to the class of incretin mimetics, such as the GLP-1 agonists semaglutide and liraglutide, are FDA-approved for weight loss therapy in overweight and obese individuals.

More specifically, they are approved for chronic weight management alongside lifestyle modification in adults with obesity or overweight patients (BMI>27) who have at least one obesity-related comorbidity. Liraglutide and semaglutide are also approved for use in adolescents (aged 12-17) who are classified as obese.

For example, trials in adults have shown that semaglutide can reduce baseline body weight by -9.6% to 17.4% after at least 68 weeks of therapy at the maximum dose of 2.4 mg/weekly.

The GHRH-agonist peptide tesamorelin has been shown to significantly reduce fat loss, predominantly from the abdominal region. By stimulating the secretion of GH, tesamorelin was reported to result in an 18% reduction of visceral fat on average compared to placebo in HIV patients.

Other classes of peptides, such as the enzyme inhibitor 5-Amino-1MQ are under active research as animal studies report a 30% decrease in fat cell size and a 40% decrease in fat cell volume in rodents.

Improving libido and erections

Melanocortin receptor agonists such as PT-141 have shown great potential for improving libido in women and erectile function in men.

In fact, PT-141 has received approval for addressing hypoactive sexual desire disorder (HSDD) in premenopausal women, with evidence from two phase-3 trials involving over 1000 women indicating enhanced libido and lessened discomfort during intimacy.

In a separate study focusing on men with erectile dysfunction, a notable enhancement in erections was observed in 33.5% of participants who received PT-141 after 45 minutes, in contrast to the 8.5% in the placebo cohort.

Stimulating muscle growth and bone mass

Peptides that stimulate the release of GH have also been noted to result in increased muscle and bone mass after prolonged therapy. That is primarily due to the anabolic effects of GH and its mediator – IGF-1.

For example, tesamorelin trials in HIV patients have reported that the peptide can significantly reduce the muscle wasting associated with AIDS and even increase muscle density and muscle size in certain areas.

Sermorelin has also been reported to cause a 1.26 kg increase in lean mass after 16 weeks of therapy in healthy older individuals.

GHS has also been suggested to increase muscle mass by stimulating GH release but also increasing appetite.

The GHS called MK-677 (ibutamoren) has been reported to cause a significant increase in both muscle mass and bone mass without affecting fat mass in clinical settings.

MK-677 is a peptidomimetic with a non-peptide structure and a similar mechanism of action as the peptide-based compounds in the GHS class. However, there aren’t any GHS that are currently approved for human use.

Enhancing tissue healing

Several peptides are under active research. Some of the most notable examples included the naturally occurring peptide thymosin beta-4 and its fragment called TB-500.

Studies suggest that thymosin beta-4 may help facilitate the healing of tissues by stimulating cellular motility, reducing inflammation, and increasing the formation of new blood vessels.

The peptide has been tested in phase-2 clinical trials for dry eye management and has shown a significant reduction in secondary parameters related to discomfort. The peptide is also under investigation for its potential antifibrotic properties and healing effects on cardiac muscle.

Promoting skin health

A diverse range of peptides have been reported to have potential benefits for skincare.

For example, the GHRH-mimetic sermorelin has been reported to significantly increase skin thickness and combat the age-related thinning of the skin in both male and female patients.

Other peptides, such as the copper tripeptide GHK-Cu have also been studied regarding their effects on skin health, and it’s also a common ingredient in many topical formulations for skincare.

For example, one trial, which included forty females aged 40-65 years, reported that topical GHK-Cu application resulted in a reduced wrinkle volume by 55.8% and wrinkle depth by 32.8%.

Peptides side effects

Similar to most other medications, peptides are not free of side effects. Yet, the majority of peptides that are approved for human use have favorable safety profiles thanks to their specificity and selectivity.

Most Peptides Have Specific Side Effects (Usually Mild and Rare)

Some of the most common side effects are related to the route of administration, which is usually subcutaneous. Subcutaneous injections are generally safe but may lead to mild transitory side effects at the injection site, such as:

  • pain and discomfort
  • redness
  • bleeding
  • swelling
  • self-limiting infections


Further, most peptides have specific side effects related to their pharmacokinetics and pharmacodynamics.

For example, FDA-approved GHRH-mimetics such as tesamorelin are associated only with transitory edema-related reactions such as swelling in the legs, joint pain, and carpal tunnel syndrome.

Rarely, some patients may also complain of facial flushing, palpitations, or hypersensitivity reactions such as rashes.

Another FDA-approved peptide, PT-141, is associated primarily with mild side effects when used according to the official guidelines (up to 8 times a month). Research reports of nausea, flushing, headaches, and a modest, transitory increase in blood pressure.

GLP-1 agonists such as semaglutide and liraglutide have also been tested extensively by phase-3 studies which showcase a favorable safety profile and side effects primarily constituting transitory gastrointestinal problems. Serious side effects such as self-limiting pancreatitis are extremely rare.

The aforementioned side effects during peptide therapy can be minimized or even completely avoided by proper dosing and monitoring from an experienced medical doctor.

Although most FDA-regulated peptides appear to be well-tolerated and produce minimum side effects in clinical trials, none have been approved in pregnant and lactating women. That is either due to concerns from animal studies or lack of any safety data at all.

How to take peptides safely

Peptides must be stored, dosed, and administered properly in order to ensure their safety and effectiveness as therapeutic agents.


The majority of peptide-based drugs can be administered only via injections. This is attributed to their susceptibility to rapid degradation in the gastrointestinal tract when ingested and their inability to penetrate the skin due to their molecular size and polarity.

The preferred method for injecting peptides is via subcutaneous injections, as it is associated with less pain, risks, and discomfort. Studies also suggest that the maximum volume generally accepted for subcutaneous injections is 1.5ml. The most suitable areas for subcutaneous injections include:

  • Abdominal area, at least 2 inches from the navel
  • Front outer thighs
  • Outer upper arms
  • Lower loins


Usually, the abdominal area is the most preferred zone as it is associated with the least amount of discomfort.


The specific dose to be injected will depend on the peptide and the official guidelines related to its use.

For example, GLP-1 agonists such as semaglutide must be initiated at doses as low as 0.25mg/weekly, which are gradually increased every four weeks up to 2.4mg/weekly in order to minimize the risk of side effects.

Other peptides, such as PT-141, can be taken at the maximum daily dose of 1.75mg, but they must not be administered more than once per day or eight times a month.


Furthermore, peptides must be stored properly in order to ensure that they remain viable and effective throughout the course of the therapy.

Most FDA-approved peptides are available as auto-injector devices which contain the peptide dissolved into a sterile solvent that also contains preservatives.

These devices should be stored in a refrigerator at 36 to 46 degrees F (2 to 8 degrees C) before first use and either refrigerated or kept at room temperature for up to 28 days after first use.

In addition, peptides are also available as lyophilized powders, which need to be reconstituted manually with a solvent before use. In their lyophilized state, peptides can be stored for several years without a significant risk of degradation.

Once reconstituted, the shelf-life of these peptides will depend primarily on the selected solvent. Usually, bacteriostatic water, which contains 0.9% benzyl alcohol as a preservative, is the preferred choice, as it provides reconstituted peptides with up to 28 days of shelf life when refrigerated at 36 to 46 degrees F (2 to 8 degrees C).

Peptides should never be frozen, heated, exposed to direct sunlight, or shaken/stirred, as these factors can easily damage the peptide bonds within its structure and inactivate the medication.

Are peptides safe?

Numerous therapeutic peptides are approved by the FDA as safe for human use. These include peptides shown as effective by scientific data for benefiting weight loss, muscle growth, skin health, and more.

The safety of peptide therapy also requires following the official recommendations for dosage and administration. For example, some peptides, such as the GHRH-agonist tesamorelin, are safe for use when administered every day for prolonged periods of time, as shown by trials lasting up to 12 months.

Other peptides, such as the GLP-1 agonist semaglutide, are meant for once-weekly administration, and the dosage must be carefully titrated to reduce the risk of side effects. Yet, they have been safely administered for up to 104 weeks at a maximum dosage of 2.4 mg/weekly.

Some peptides, such as PT-141, should not be used daily for more than 8 days per month, as prolonged exposure can increase the risk of undesired side effects such as focal hyperpigmentation.

Improper use of therapeutic peptides, including overuse, can compromise their effectiveness and lead to safety concerns. Furthermore, peptides that are not legally obtained from licensed pharmacies are not subject of control by regulatory bodies.

Using such compounds can hide serious health risks, as they may be diluted, contaminated, expired, or tampered with in any other way that compromises their safety.

Therefore, always consult with a licensed medical doctor before initiating peptide therapy, and make sure to obtain your peptides from reputable sources.