You’re training hard and nothing is moving. Here’s what the evidence actually shows.
You lift four or five days a week. You eat like you mean it. And somewhere in the last couple of years, the returns stopped arriving — the same weight, the same mirror, month after month. That is the moment the peptide market has been waiting for, and it has a very confident answer ready. This page gives you the unconfident one: what the human trials in this category actually measured, what they found, and what usually turns out to be the real limiter in a man who is already doing the work.
Castellano Health Institute · Serving Orange County
A message to a system — not a substance that adds muscle.
Peptides are short chains of amino acids that the body uses as signaling molecules — internal messages telling specific cells to do specific things. The family marketed for muscle and body composition works by signaling the pituitary to support the body’s own production, rather than introducing an outside hormone at an outside dose.
That mechanism is the whole story, and it cuts both ways. It is why this category is not anabolic steroid use in a friendlier package: nothing here is pushing you 10 to 100 times past your own physiology, and the side-effect profile is nothing like it. It is also why the effect size is small. You are nudging a process your body already runs, within the range it already runs it. A nudge to a working system produces a nudge-sized result — which is exactly what the trials found.
Further down, the individual compounds get named and described — you deserve to know what the words mean and what the public record says about each one. Naming them is not the same as recommending them. What is appropriate to compound and prescribe shifts with current regulatory guidance, and what fits a particular man depends on what his bloodwork says, so that decision stays in the visit. The broader category map lives on the peptide therapy page.
Lean mass and strength are not the same finding.
“Does it work” is the wrong shape of question, because the answer changes depending on which outcome you ask about. Here is where each level of the evidence currently sits.
| Where the evidence sits | What has actually been shown | How it’s treated here |
|---|---|---|
| Randomized human trials — body composition | A two-year placebo-controlled trial of 65 healthy older adults, published in Annals of Internal Medicine in 2008, found fat-free mass over the first 12 months rose about 1.1 kg on the compound versus a 0.5 kg loss on placebo. | Taken seriously. This is the strongest human signal the category has, and it is genuinely a signal. |
| Randomized human trials — strength and function | The same 2008 trial reports directly that the increase in fat-free mass did not result in changes in strength or function. | Treated as the headline, not the footnote. A scan number is not a performance outcome, and the two get conflated on purpose in this market. |
| Tissue-repair and recovery compounds | Mostly cell and animal models. The human work is a small number of uncontrolled reports. | Read as hypothesis-generating. Uncontrolled results are the kind that most often fail to survive a proper trial. |
| Dose, duration, and who it is for | Not established in the published literature for muscle-focused use in healthy adults. Several compounds in this space also sit on FDA's public list of substances nominated for compounding that the agency has flagged for potential significant safety risks. | A reason for conservative, time-limited protocols with a scheduled re-evaluation — never indefinite use, and never without oversight. |
| Training load, protein, sleep, and correcting a measured deficiency | The strongest evidence base in the whole conversation, and the least marketed. Correcting a documented testosterone deficiency raised lean body mass by a pooled 1.22 kg across 16 randomized placebo-controlled trials. | The foundation. Nothing in the peptide category substitutes for it, and adjuncts are only worth discussing once it's in place. |
The single most useful study in this category is worth reading closely rather than in summary. In a randomized, placebo-controlled trial of 65 healthy older adults published in Annals of Internal Medicine in 2008, twelve months of MK-677 — the oral secretagogue also known as ibutamoren, and the most-studied compound in this family — raised fat-free mass by about 1.1 kg while the placebo group lost about 0.5 kg. That is a real result and the authors report it as one. They also report, in the same conclusion, that the increased fat-free mass did not result in changes in strength or function. Both halves of that sentence are the finding. Only the first half makes it into the advertising.
For contrast, look at what an unambiguous muscle effect looks like in the literature. A 1996 randomized trial in the New England Journal of Medicine assigned 43 men to four groups — placebo or 600 mg of testosterone enanthate weekly, each with or without a supervised strength-training program, for ten weeks. Those supraphysiologic doses increased fat-free mass, muscle size, and strength, especially in combination with training. That is what a large effect reads like in a paper: multiple outcomes moving together, including the ones you can measure under a bar. The peptide literature does not look like that, and honest reading means saying so out loud.
Sermorelin is the one member of this family with a genuine regulatory history, which is worth knowing precisely because almost nothing else in the category has one. It was an FDA-approved prescription drug — approved in December 1990 as a diagnostic agent for assessing pituitary secretory capacity, and again in September 1997 for a narrow pediatric endocrine indication. Its manufacturer discontinued both products in 2008 and FDA withdrew the approvals in June 2009. In 2013 the agency formally determined that they “were not withdrawn from sale for reasons of safety or effectiveness” (78 FR 14095). Read that carefully, because it is regularly oversold in both directions. It means a business decision ended the product, not a safety finding — and it also means the approvals that existed were for a diagnostic test and a pediatric condition. Neither was for building muscle in a healthy adult. This is background, not a recommendation.
The regulatory picture around the rest of the category deserves the same plain reading, and it is a matter of public record. FDA maintains a published list of bulk drug substances nominated for pharmacy compounding that it has flagged for potential significant safety risks, and most of the names in this market appear on it. For several, the agency’s stated reason is not that harm has been demonstrated — it is that it “lacks sufficient information to know whether the drug would cause harm when administered to humans.” “We don’t know yet” is not the same sentence as “safe,” and a man about to inject something deserves to know which sentence applies to what he is holding. So here are the actual names.
What each one is, and where it actually stands.
You are going to encounter these names, so you may as well encounter them with the regulatory record attached. What follows is reference, not a catalogue: it describes what each compound is, what the community uses it for, and what FDA has published about it. Read the right-hand column carefully — several of these entries are the reason the category deserves more caution than its marketing suggests.
Nothing in this table is an offer, a recommendation, or a statement about what is prescribed at this practice. It is published information about compounds you will see discussed elsewhere. What might be appropriate for you specifically is a question for a physician who has read your labs.
| Compound | What it is | Where it stands with FDA |
|---|---|---|
| Ibutamoren (MK-677) | An orally active secretagogue that acts at the ghrelin receptor to signal the pituitary. It is the most-studied compound in this family in humans. | On FDA's compounding safety-risk list under both 503A and 503B. FDA cites a randomized placebo-controlled trial in hip-fracture patients that was terminated early over a congestive heart failure safety signal; those authors concluded the compound had an unfavorable safety profile in that population. |
| Ipamorelin | An injectable secretagogue in the same receptor family, widely discussed in the community for body composition. | On FDA's list under 503B. FDA flags immunogenicity risk, notes it contains unnatural amino acids that complicate characterization, and cites published serious adverse events including death when it was administered intravenously for a gastric-motility indication. |
| CJC-1295 | A long-acting analog of the hypothalamic releasing hormone that signals the pituitary — a different mechanism from the secretagogues above, aimed at the same axis. | Was on FDA's safety-risk list; the nomination was later withdrawn by the party that submitted it. FDA's published concerns remain listed: serious adverse events including increased heart rate and systemic vasodilatory reaction, with limited available clinical data. |
| Sermorelin | The same releasing-hormone mechanism, short-acting. The one compound in this family that was once an approved prescription drug — see the note above. | Approved 1990 and 1997 for a diagnostic use and a pediatric endocrine indication; discontinued commercially in 2008, approvals withdrawn 2009. FDA determined in 2013 that it was not withdrawn for reasons of safety or effectiveness. |
| BPC-157 | Not a muscle-building compound at all — a repair-and-recovery peptide that gets pulled into this conversation because the same people sell it. | Was on FDA's safety-risk list; nomination later withdrawn by the nominator. FDA's published concern stands: it identified no, or only limited, safety information, and "lacks sufficient information to know whether the drug would cause harm when administered to humans." |
| TB-500 (thymosin beta-4 fragment) | Another repair-oriented peptide, marketed alongside the muscle compounds rather than being one. | Was on FDA's safety-risk list; nomination later withdrawn. FDA states it has not identified any human exposure data for drug products containing this fragment by any route. |
| AOD-9604 | A fragment marketed for fat loss and body recomposition, which is why it turns up in muscle-focused stacks. | Was on FDA's safety-risk list; nomination later withdrawn. FDA identified no, or only limited, safety information and also identified serious adverse events that may be associated with it, though causality is not clear. |
Statuses above are drawn from FDA’s published compounding safety-risk lists. Note the distinction the list itself draws: a withdrawn nomination means the party who submitted the substance for consideration withdrew it — not that FDA resolved its concern. The agency’s stated concerns remain published in both cases.
Before you add something, find out what’s missing.
Here is the pattern Dr. Castellano sees constantly. A man in his forties or fifties who trains seriously, whose lifts stalled and then slid, who is recovering worse than he used to and carrying weight he didn’t used to carry — and who has never had his testosterone measured. He is shopping for something to add when the actual problem is something that left.
That is not a rare scenario. In the HIM study, published in the International Journal of Clinical Practice in 2006, 38.7% of men aged 45 and older presenting to primary care offices met the criteria for hypogonadism. Nearly four in ten. And unlike everything else on this page, that one is a blood draw away from an answer.
What restoring a documented deficiency does is also measured rather than promised. Across 16 randomized placebo-controlled trials pooled in a 2016 meta-analysis, testosterone replacement in men with hypogonadism increased lean body mass by 1.22 kg (95% CI 0.33 to 2.11). Honest reading means saying what that isn’t, too: in the Testosterone Trials, published in the New England Journal of Medicine in 2016, 790 men aged 65 and older with levels under 275 ng/dL were treated for a year, and the Physical Function Trial’s primary outcome — the share of men whose six-minute walking distance improved by at least 50 metres — was not significantly different from placebo. Treating a deficiency is not a performance program. It is correcting a documented deficit, and the honest claim stops there.
The reason it still comes first is simple: it is the one variable in this whole conversation that can be measured, named, and corrected, and the one where the evidence is strongest. What that evaluation looks like is laid out on the low testosterone page, and the treatment itself on the TRT page. Which of the two paths is load-bearing for you is worked through on peptides versus TRT.
Five things that stall a man who is already doing the work.
This is the list a visit works through before anything gets prescribed. Four of the five cost nothing to investigate, and the fifth is a blood draw:
- An undiagnosed testosterone deficiency — measurable, diagnosable, and the most common miss in men past forty
- Training that has stopped progressing in load, and has been the same program for two years
- Protein intake that is nowhere near what the training volume requires
- Sleep debt — the window where repair actually happens, which nothing replaces
- An unaddressed metabolic picture, including insulin resistance working against lean tissue
Men who have gone further down the performance road than this — and want honest medical monitoring rather than a lecture — are covered on the anabolic steroid care page. Same posture, different territory: the medical work gets done, and nobody pretends the situation is something it isn’t.
The door is open. It just opens in the visit.
Nothing above is an argument that peptide therapy is off the table. Peptide therapy at Castellano Health Institute is offered, physician-supervised, and decided case by case. Whether a peptide protocol has a place in your plan — and which one, if any — is a one-on-one conversation with Dr. Castellano against your labs and your history. That decision belongs to a physician who has read your bloodwork, not to a page on the internet, and that is the reason there is no menu here.
What the practice does rule out is the model this category is best known for: an online order, a monthly auto-shipment, no lab rechecks, and nobody reading the results. That is not peptide therapy under medical management. When a protocol does belong in a plan, it runs the way everything else here runs — labs first, a defined block, then a genuine re-evaluation against how you are actually doing. If nothing meaningful has changed at the checkpoint, it changes or it stops. The safety and oversight side of the category is broken down on are peptides safe.
Dr. Castellano is board certified by the American Board of Family Medicine and the American Board of Anti-Aging & Regenerative Medicine, and he practices solo by design — the physician who reads your first panel is the one reading your fourth. Call the office to schedule a consultation and get an actual answer about your own situation.
What men actually ask about this.
Don’t see yours? Call the office and ask Dr. Castellano directly.
Do peptides build muscle?
Why does a peptide consultation start with testosterone?
Does that mean Dr. Castellano won't prescribe peptides?
What about BPC-157 and TB-500 — the ones people talk about on forums?
I already train hard and eat well. Isn't a peptide the logical next step?
How is this different from anabolic steroids?
Do I need labs before any of this?
What does the first visit actually look like?
Related in the peptides knowledge cluster.
Peptide Therapy with Dr. Castellano
The service page — the categories, the honest primer, and how a protocol gets evaluated.
Peptides vs. TRT
Which problem each one actually solves — and which is load-bearing for you.
Peptides for Healing & Recovery
The tissue-repair side of the category, and how thin the human evidence really is.
Anabolic Steroid Care
Honest medical monitoring for men running supraphysiologic protocols — no lecture.
Low Testosterone
The symptoms, the evaluation, and what the numbers actually mean.
Are Peptides Safe?
Side effects, oversight, and where the risk in this category actually sits.
Find out what’s actually capping you.
A man who has stopped progressing deserves a diagnosis before he deserves a product. Call the office to schedule a consultation — a one-hour sit-down with Dr. Castellano, with your bloodwork on the table. If peptide therapy is a reasonable part of the answer for you, you’ll hear exactly where the evidence for it stands. If your testosterone is the problem, you’ll hear that first. And if the honest answer is that your training program is the problem, you’ll hear that too.
Mon–Fri 9 AM – 5 PM· Serving Orange County