The fundamentals, without the noise.

Amino acids are the 20 standard building blocks of every protein in your body. Link a few of them with peptide bonds and you have a peptide. Chains of roughly 2 to 50 amino acids usually get called peptides. Longer chains that fold into a stable 3D shape are proteins. The line is a naming convention, not physics. Insulin, at 51 amino acids, gets called both.

Your body already runs on peptides. Insulin, glucagon, GLP-1, oxytocin and vasopressin are all peptide hormones. Most compounds in this atlas are either copies of a natural fragment (BPC-157 is 15 amino acids from a gastric protein) or engineered analogs built to last longer in the blood. Semaglutide carries a fatty-acid side chain that binds albumin, which stretches its half-life to about a week.

Two practical consequences. First, peptides are fragile. Digestive enzymes cut peptide bonds, so most have to be injected to reach the blood intact. Second, they are easy to make badly. A missing amino acid, a truncated chain or leftover solvent is invisible to the eye and only shows up in lab testing.

Bioavailability is the fraction of a dose that reaches circulation intact. An IV dose is 100% by definition. A swallowed peptide usually lands close to zero, because the gut treats it like the protein in your lunch and digests it.

Oral semaglutide is the famous exception, and it proves the rule. It only works with an absorption enhancer (SNAC), and its label still puts oral bioavailability at roughly 0.4–1%. That is why the daily oral doses are measured in milligrams while the weekly injection doses are a fraction of that.

Claims that a research peptide is “orally stable” usually rest on lab tests in simulated gastric juice, not on blood levels measured in people. Stable in a test tube and absorbed by a human are two different findings.

Continuous means steady exposure for as long as a drug is used. Cycling means blocks of use separated by breaks. Titration means starting low and stepping the dose up over weeks.

There are real reasons a schedule can matter. Receptors can become less responsive under constant stimulation (tachyphylaxis). The growth hormone axis is pulsatile by nature, so a steady signal is not the same as a normal rhythm. And titration gives side effects time to settle. The GLP-1 labels step doses up in 4-week increments for that reason.

Now the contrarian part. For most research peptides, the on/off pattern did not come from a trial. It came from forums, clinic handouts and bodybuilding tradition. “Four weeks on, two off” can be a sensible guess and still be a guess. Where a schedule comes from a label or a trial, the dossier says so. Where it does not, it carries the commonly reported label.

Drugs for chronic conditions are usually studied as continuous therapy. In semaglutide trials that switched people to placebo, much of the lost weight came back. A break is not automatically the safer or smarter option. It is a different experiment.

Every dossier carries a grade from A to D. It reflects the best human evidence for the uses that dossier covers. When the popular use runs ahead of the data, the evidence note says so on the first screen.

The glow scales with evidence strength. A gets the brightest treatment, B less, and C and D get none at all. A thin evidence base should never look like a gold star.

Many peptides ship as a freeze-dried (lyophilized) powder because they are far more stable dry. Reconstitution means dissolving that powder in a sterile liquid so it can be measured.

Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that slows bacterial growth after a vial has been punctured. Plain sterile water for injection has no preservative and is meant for single use. Neither one makes a contaminated product clean.

Concentration math is where small mistakes become big ones. The same powder in twice the water gives half the concentration, so the same mark on a syringe delivers half as much. Insulin syringes are graduated in units, not milligrams, which adds a second conversion. One slipped decimal is a tenfold error.

Sterility is a medical skill. Clinics rely on aseptic technique, trained staff and pharmacy-grade products because contamination and injection-site infections are real. Gray-market vials add unknowns that no technique fixes. Nobody has verified the contents, the amount or the sterility.

Peptides break down through ordinary chemistry: oxidation, deamidation, hydrolysis and clumping (aggregation). Heat speeds all of it up. Light, especially UV, damages some amino acids directly. Water is the medium most of these reactions need, which is why a dry powder usually outlasts a solution.

Once a powder is dissolved, the clock runs faster. Approved products print storage rules and discard dates for a reason. Egrifta WR, for example, is labeled for use over 7 days once its vial is reconstituted. Freeze-thaw cycles and vigorous shaking can damage some peptides too.

For research-market products, claims like “stable for months at room temperature” are rarely backed by published stability data. Because breakdown products look like nothing, “it looked fine” tells you very little.

FDA-approved means a specific product, for a specific indication, at labeled doses, made under inspected manufacturing. Approval does not extend to popular off-label uses, and it never extends to a gray-market powder that happens to share the name.

Investigational means in formal clinical development, or approved elsewhere but not in the US. Retatrutide has large randomized trials behind it and is still not approved anywhere. Thymosin alpha-1 is sold as Zadaxin in dozens of countries and is not FDA-approved.

Research discussion means no approval that applies here. These compounds are often sold labeled “for research use only, not for human consumption.” That label is a legal posture, not a quality standard.

Under section 503A, a pharmacy can compound from a bulk ingredient only if it clears one of a few bars: the ingredient is a component of an FDA-approved drug, it has a USP monograph, or it appears on FDA's 503A bulks list. Most research peptides clear none of them, so the bulks list is the door everyone is watching.