AS THE CURIOSITY around peptides grows, the FDA has considered removing a portion of the 19 synthetic peptides from the Category 2 Bulk Substances List. This is kind of a huge deal because when the FDA classifies a substance as Category 2 they believe that it carries significant safety risks. In July of this year, a panel will evaluate evidence for seven synthetic peptides, with another five under review in 2027.
Sritha Rajupet, MD, MPH, chair of the department of family, population, and preventive medicine at Stony Brook Medicine, has concerns. “Most of these peptides still lack high-quality human data on safety, effectiveness, and appropriate dosing,” Dr. Rajupet says. Meaning, despite chatter that the FDA may remove the Category 2 label, there’s still not a lot of research around if and how they work—along with any side effects.
Still, Dr. Rajupet acknowledges that people are interested in synthetic peptides—and many are already obtaining them through unregulated channels.
Kent Bradley, MD, sees this at his role of chief medical officer at 10X Health, which offers synthetic peptide therapy. “Many of the people reaching for peptides have already exhausted conventional options,” he says. “The issue we are seeing is that individuals may have gotten a peptide without going through legitimate quality checks of a compounded pharmacy and self-administering based on information they are seeing off of social media.”
The world of synthetic peptides is promising, for sure. But there are dangers—some of which are serious (ahem, cancer). Dr. Rajupet says that in order for consumers to protect themselves, they have to study up.
“From a clinical perspective, the priority is balancing harm reduction with scientific rigor—engaging patients in open, nonjudgmental conversations while being clear that many of these therapies remain experimental, with uncertain risks and benefits,” says Dr. Rajupet.
For this reason, we created a one-stop glossary to help answer your questions about the current peptide-palooza we’re in now. Here’s the hype—and actual science.
First, What Are Peptides?
WELL, KNOW THAT peptides exist naturally. Technically, they’re short chains of amino acids, the building blocks of protein. And not just the kind of protein that builds biceps. Proteins can also act as messengers throughout your body, doing everything from signaling the release a particular hormone to regulating inflammatory responses.
But when we’re talking about the kind of peptides the FDA will consider for deregulation, we’re talking about synthetic peptides delivered through sprays or injection. These drugs work to trigger the same responses as natural peptides, but the science is in its very early stages. Anecdotal evidence from who take peptides have reported improvements in their health, appearance, and muscle performance. But, again, anecdotal.
The 12 Peptides That May Be Legal
These are the synthetic peptides that the FDA will consider for deregulation in 2026 and 2027, broken into categories based on their supposed health benefits.
Metabolic Health
AOD-9604 (Anti-Obesity Drug 9604)
Known as the fat burning peptide, AOD-9604 mimics human growth hormone to promote lipolysis, or the breakdown of stored fat. Scientists are using the peptide as a possible treatment for obesity and people are taking the peptide recreationally to burn body fat, boost fat metabolism, and support body recomposition. There is also discussion of AOD-9604 helping with joint pain, mobility, and collagen production. One of the supposed benefits of AOD-9604 is that it sheds fat without affecting blood sugar or inducing insulin resistance.
Research summary: The studies on the effectiveness and safety of AOD-9604 go back roughly a decade. The research was largely conducted on animals and most of the studies that showed positive results were funded or led by researchers from the pharmaceutical company that developed AOD-9604.
- A 2001 study found the AOD-9604 peptide increased metabolism and reduced fat in rodent models of obesity.
- A 2007 study on AOD-9604’s effectiveness found in a 12-week clinical trial that people injected with (1 mg/d) of AOD-9604 lost an average of 5.7 pounds compared to 1.7 pounds in the placebo group. However, people with higher doses (10 mg/d) did not lose more weight.
- In 2007, a phase 2 clinical trial testing the effectiveness of AOD-9604 in humans failed to show significant weight loss in a 24-week trial involving 536 people. The clinical development of AOD-9604 was discontinued.
- A 2013 study reviewed 6 trials in people who were obese (excluding one) and were injected with the AOD-9604 peptide and reported the peptide generally well-tolerated with no adverse effects or drug-related withdrawals. However, there were five cases where people developed skin cancer though the researchers did not link it to the study medication for two reasons. One, cancer did not occur in the group with the highest peptide dose. Two, the people who developed cancer “neglected their personal medical care for a longer period of time.”
- Also important to note is that AOD-9604 was developed by Metabolic Pharmaceuticals who also funded all six clinical trials. Several researchers are stockholders and are employees of Metabolic Pharmaceuticals.
- AOD-9604 has been tested for repairing damaged joint cartilage in people with osteoarthritis. A 2015 study on rabbits showed that the peptide helped with cartilage regeneration with an increased effectiveness when paired with hyaluronic acid.
MOTS-C
This peptide reportedly protects the cell by providing more “fuel” for increased stamina. So people who report fatigue are taking the peptide to improve energy and metabolism. Because MOTS-C is supposed to target mitochondria, the energy sources of a cell, you’ll see it promoted in longevity stacks.
Research summary: While there has been extensive research into the physiological function of MOTS-C, there is a lack of clinical trial data testing the safety and effectiveness of the peptide.
- Animal studies have found the MOTS-C peptide is helpful in stopping insulin resistance and diet-induced obesity.
- A 2021 study in mice found that MOTS-C injections increased physical performance compared to untreated mice of the same age, including those fed a high-fat diet. Aged mice (meant to be the equivalent of a person 65 and above) treated with MOTS-C showed physical improvement in their grip strength and gait.
- The same researchers also collected and analyzed the skeletal muscle tissue from young men before, during, and after exercising. Their MOTSC-c increased nearly 12-fold after exercise and remained high after resting for four hours. However, the men were not injected with a peptide. Instead, the researchers only observed natural changes in MOTS-C levels.
- Scientists are currently recruiting people for a 12-week clinical trial to test the effectiveness of MOTS-C in adults with obesity and prediabetes.
Cognition
Semax
Semax is considered a brain-boosting peptide often given as a nasal spray. Anecdotal reports detail improvements in memory, attention, and deeper mental awareness. Semax is supposed to work by raising a protein called brain-derived neurotrophic factor (BDNF) that is important for learning and strengthening connection between brain cells.
Research summary: Most of the research in Semax that claims it has neuroprotective effects come from Russia, where the peptide is used in the treatment of people with stroke. The Alzheimer’s Drug Discovery Foundation reviewed the Russian pilot studies in humans and found a lack of strong evidence demonstrating that Semax would improve cognition in healthy individuals or in the prevention of cognitive aging. (Although a recent 2025 study from Russia found evidence of Semax injections reducing amyloid plaques in rat models of Alzheimer’s). Older studies using rats found improved cognition 15 minutes after injection, likely by stimulating BDNF production. There is a lack of safety data, especially in long-term side effects, in humans. One review reported discoloration of the nasal cavity and increased blood sugar levels in people with diabetes. Not great.
Selank
Selank is a nootropic touted for reducing anxiety and stress while increasing cognitive performance. Anecdotal evidence calls Selank a “life-changer” for anxiety and sleep, with some people feeling relaxed but not drowsy, as well as more focused.
Research summary: Selank’s anxiolytic and cognitive protective effect along with relieving stress have only been studied in rodents and molecular studies. Older mice studies have also found evidence of improved learning and memory performance after a single injection of Selank.
Muscle Tissue & Injury Recovery
TB-500 (Fragment of Thymosin Beta-4)
TB-500 is a peptide intended for muscle recovery, increased flexibility, and joint stability. Users often pair the synthetic peptide with BPC-157 to further boost muscle recovery. TB-500 works by binding to a structural protein in cells called actin. By up-regulating actin, TB-500 purportedly speeds cell movement for tissue repair.
Research summary: There is a good amount of animal research on Thymosin Beta-4 and its accelerated healing effects on skin and muscle fibers. While there is a body of preclinical research on the peptide, there’s a lack of studies looking at the synthetic peptide TB-500. Plus, there is no clinical evidence in humans that Thymosin Beta-4 or TB-500 repairs muscles or increases athletic performance.
More concerning are studies linking elevated Thymosin Beta-4 levels with the development of cancer. Through the same mechanisms that promote wound healing, Thymosin Beta-4 may enhance tumor angiogenesis, the process where cancer cells stimulate new blood vessels, which provides them oxygen and nutrients to grow and spread.
BPC-157
Known as the “Wolverine” or “Body Protection Compound,” the synthetic peptide reportedly helps with tissue repair and anti-inflammatory effects. Users champion the peptide’s ability to speed recovery from intensive workouts or even injury. BPC-157does not directly build muscle mass.
Research summary: Animal data on BPC-157 showed evidence of the peptide helping with musculoskeletal injuries. However, there is little data showing the effects in humans.
- A 2025 review identified 36 studies published between 1993 and 2024 with 35 being animal experiments and only one in humans. In animals, BPC-157 boosted growth factors, reduced inflammation, and improved injury in muscles and tissues.
- In a small 2021 study in humans, people injected with BPC-157 for knee pain—or a combination of BPC-157 with another peptide, thymosin-beta-4—linked a decrease in knee pain for almost all the study participants. That said, the study did not provide a control group for proper comparison and relied solely on the patient’s subjective recall of knee pain rather than any other objective measure.
Immunity
Thymosin Alpha-1
The natural form of this peptide helps with increasing and restoring immune function. It works by enhancing antibody response and T-cell activity. People taking the synthetic, injectable form report immediate improvement in their well-being after long COVID and other immune disorders. Outside of the US, Thymosin Alpha-1 is approved in over 30 countries for treating hepatitis and other infections.
Research summary: Five large clinical trials on the peptide have found Thymosin Alpha-1 reduces inflammation and infection in people with severe acute pancreatitis. That’s likely due to the peptide’s ability to rebalance immune cell distribution, including boosting the percentages of CD4+ T cells. Thymosin Alpha-1 has also been shown to enhance vaccine response and help people with severe COVID by repairing damage caused by inflammation. However, one large phase 3 clinical trial in people with sepsis found an injection of thymosin alpha 1 did not improve mortality outcomes.
KPV
People taking the synthetic form of this peptide report doing so to reduce inflammation and improve skin health. (Some say it can clear up eczema, psoriasis, and acne.) There are also some people with inflammatory bowel conditions, such as Crohn’s and IBD, who say that KPV has helped their gut health. The peptide reportedly works by inhibiting several pro-inflammatory pathways while preserving other immune responses.
Research summary: There’s not sufficient data on KPV to conclusively say it helps in humans. The most cited research on KPV is a 2008 study, which found that the peptide reduced intestinal inflammation in human intestinal cells. Yes, that was many, many years ago.
Hormones and Sleep
Emideltide (DSIP)
This neuropeptide reportedly promotes falling asleep faster, as well as increasing how much time you spend in restorative deep, slow-wave sleep. in Stage 3 sleep. Anecdotal evidence of people taking the synthetic form of this peptide states that in helps with staying asleep, increasing sleep duration, and entering deep sleep.
Research summary: DSIP research on humans is extremely limited. Most research looking into DSIP’s role in sleep took place in the 1980s and 1990s—with mixed results. While a small clinical trial did report sleep-promoting effects, other studies found it ineffective or from a placebo effect. Research in the 2000s has been focused on animals and how DSIP could help protect against cancer or improve motor ability after stroke.
Kisspeptin-10 (Kp-10)
This peptide has links to sexual function. It works by stimulating the release of the hormone, gonadotropin, which results in an increase of testosterone. People who take synthetic kisspeptin-10 have reported a greater libido, ability to maintain an erection, and enjoy orgasm, along with reduced anxiety—especially surrounding sexual response.
Research summary: There is animal and human research that shows kisspeptin-10 stimulates gonadotrophin release. Most notably, a small clinical trial found that men with low sexual desire experienced increases in “penile tumescence” (their term, not ours), as well as greater attraction and arousal. There were no side effects reported.
Longevity and Looks
Epitalon (Epithalamin)
Epitalon is the natural form of the peptide, and it’s been used to treat chronic insomnia, especially in people who don’t respond to sleep medications. By raising melatonin, the peptide would allegedly regulate circadian rhythms and promote better sleep. Epithalamin is the synthetic peptide and people are reportedly taking it for anti-aging effects, both cognitive and aesthetic.
Research summary: Epitalon has not been tested in people for slowing or preventing cognitive decline. Most of the early preclinical and clinical studies on epitalon’s effects on anti-aging, cognition, and sleep come from Russia and mainly from the lab of the now-deceased Dr. Vladimir Kh. Khavinson. The few studies in human cells (note, not actual humans) suggest that epitalon extends telomere length. Telomeres are the protective caps at the end of chromosomes to protect from damage. In terms of safety, there is a lack of data, especially on its short-term and long-term toxicity effects.
GHK-Cu (Copper Peptide)
The natural GHK-Cu peptide is used for promoting skin health. People using the synthetic drug are using GHK-Cu to stimulate collagen and elastin production to tighten aging skin, reduce wrinkles, fade scars, and repair the skin barrier. People have anecdotally reported thicker, fuller hair after using the peptide as it supposedly reduces inflammation and increases blood circulation to the scalp.
Research summary: Topical GHK-Cu is commonly used in cosmetics to increase collagen production, promote wound healing, and improve skin health. It has a good safety profile because it has limited low-level skin absorption. Injectable and oral versions of GHK-Cu may come with several potentially life-threatening risks.
- A 2019 review looking at the effects of copper ingestion found the potential of free copper ions that may cause gastrointestinal and liver toxicity.
- In the joint, excess copper could impair mitochondrial integrity and create an oxidative stress environment that kills chondrocytes (healthy cells in cartilage).
Two More Peptides Creating Discussion
Ipamorelin
This peptide is a selective agonist of the ghrelin/growth hormone secretagogue receptor (GHSR1) that stimulates the pituitary gland to release growth hormone production. (Yeah, it’s complex.) Just know that people are excited about Ipamorelin because the peptide reportedly increases muscle mass and strength.
Online forums dedicated to Ipamorelin mention that taking the peptide does not increase appetite, cortisol, or prolactin like other growth hormone peptides. In addition to strength improvements, other ancedotes discuss skin and hair benefits. Ipamorelin is typically paired with other peptides, such as CJC-1295.
Research summary: Animal studies have shown that Ipamorelin is effective in stimulating the pituitary gland to release growth hormones. However, there is a lack of large clinical trials that show the peptide works in humans.
- Animal studies in the 1990s showed that Ipamorelin stimulated production of growth hormones and had similar musculoskeletal effects as other compounds that work to release growth hormones. One 2002 rat study found Ipamorelin is helpful in reversing bone mineral density loss.
- A 2014 phase II study tested the safety and efficacy of a 7-day treatment of Ipamorelin in people treating postoperative ileus (a prolonged GI issue, basically) after abdominal surgery. While the peptide was well-tolerated, results showed no difference in the outcome of the 114 adults who underwent surgery and were given 0.03 mg/kg of ipamorelin or a placebo.
CJC-1295
This peptide binds to receptors in the pituitary gland to stimulate the secretion of growth hormone and production of insulin-like growth factor 1 (IGF-1). People are taking CJC-1295 to build muscle, reduce recovery time, and increase fat metabolism. A common stack among the longevity community is CJC-1295 and Ipamorelin for its synergistic effects to maintain lean muscle, get better sleep, and reduce fatigue.
Research summary: While clinical data has shown promising results of CJC-1295 to increase growth hormone production, the peptide is linked to a number of adverse events.
- A 2006 study of CJC-1295 performed two clinical trials in people between the ages of 21 to 61. In one clinical trial where people were given a single injection of CJC-1295, there was a 2- to 10-fold increase in human growth hormone for 6 days post-injection. The second trial with multiple CJC-1295 doses showed a sustained elevation of growth hormones for up to 28 days.
- After a single injection, 94 percent of people experience mild to severe side effects compared to 29 percent in the placebo group. These included pain/irritation at the injection site for up to 5 days, headache, diarrhea, and vasodilatory responses (flushing, warmth, and temporary drops in blood pressure).
- A phase II trial of CJC-1295 that looked into treating people with obesity and HIV was terminated after a trial participant died.
5 Peptides Expected to Remain in the FDA’s Category 2 List
The following five peptides are likely to stay on the Category 2 list because of a lack of clinical evidence and/or significant safety concerns.
GHRP-2
Use: Release of growth hormones
Side effects: Infection, potential death, fluctuating blood sugar levels, pancreatitis
GHRP-6
Use: Release of growth hormones
Side effects: Increase appetite, possible changes in cortisol levels, and increases in blood sugar levels
Melanotan II
Use: “Sunless” tanning and to stimulate erections in men with erectile dysfunction
Side effects: Severe adverse events including melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome, and priapism
Cathelicidin LL-37
Use: Increasing immune defenses and fight against infections
Side effects: Nonclinical research has found adverse effects on the male reproduction system and potentially cancer development
PEG-MGF
Use: Muscle repair and recovery
Side effects: Insufficient information on whether it’s safe for humans
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