Terminology
What Is a Lyophilized Peptide?
A lyophilized peptide is a freeze-dried one: the ice is removed as vapour under vacuum, leaving a dry cake or powder that is dissolved again before use. The part most pages leave out is that the peptide is a minority of that powder. In three FDA-labeled lyophilized peptide products, the peptide accounts for 2–6.1% of the solids in the vial. The rest is inactive ingredients. This page works from the labels themselves. Research-material education only.
The short answer
- Lyophilized means freeze-dried. The material is frozen solid, then the ice is drawn off as vapour under vacuum — sublimation — instead of being boiled or evaporated with heat.
- What you get is a dry solid, described in FDA labeling as white to off-white. It may sit as a firm cake, a loose powder, or a film on the glass.
- Most of that solid is not the peptide. Across the three labeled products below the peptide is 2–6.1% of the contents; mannitol, sucrose, lactose and similar ingredients make up the rest.
- The reason for drying it is time. A peptide in solution has a far shorter shelf life than the same peptide dry.
- The formulation is part of the product. One molecule, tesamorelin, has two FDA-labeled freeze-dried formulations with different inactive ingredients and different labeled diluents.
How much of the powder is the peptide?
This is the question behind most of the surprise people describe when a vial arrives: it looks like very little, or like more than expected, or like nothing at all. The answer is printed on the labels of freeze-dried peptide medicines, which state every inactive ingredient by weight. Adding them up gives the share the peptide actually occupies.
| Labeled product | Peptide | Inactive ingredients, per label | Total solids | Peptide share |
|---|---|---|---|---|
| EGRIFTA SV (Theratechnologies) | Tesamorelin 2 mg | 20 mg mannitol, USP; 10 mg sucrose, NF; 0.78 mg histidine, USP; 0.05 mg polysorbate 20, NF | 32.8 mg | 6.1% |
| EGRIFTA WR (Theratechnologies) | Tesamorelin 11.6 mg | 145 mg hydroxypropyl betadex; 43.5 mg mannitol | 200.1 mg | 5.8% |
| Glucagon for Injection | Glucagon 1 mg | 49 mg lactose | 50 mg | 2% |
Read from DailyMed labeling on 18 September 2026 (EGRIFTA SV setid 3d783378, EGRIFTA WR setid 839334d3, Glucagon setid 789ab694). Every percentage in the table is computed from the milligram figures beside it. In none of the three does the peptide reach a tenth of the powder. The practical consequence is that the visible volume in a vial is mostly a property of the bulking agent, so it is not a way to judge content, strength or quality — two vials of equal nominal strength can look quite different if they were formulated differently.
What the inactive ingredients are doing
A milligram or two of peptide spread across the bottom of a vial would be difficult to see, difficult to reconstitute evenly, and vulnerable during drying. The ingredients that make up the rest of the solid are there to solve those problems. Mannitol (PubChem CID 6251) and lactose give the cake its body and structure; sucrose (PubChem CID 5988) is a stabiliser of the kind used to protect a molecule as the water around it is removed; histidine sets the pH; polysorbate 20 is a surfactant, which keeps material from sticking and aggregating; hydroxypropyl betadex (PubChem CID 138059664) is a cyclodextrin, a ring-shaped sugar that can hold a molecule inside it.
This is why “lyophilized peptide” describes a form, not a composition. The label of a labeled product states what else is in the vial. For research material, that information comes from the supplier’s own documentation, and where it is absent, the composition of the powder is simply unknown — the certificate of analysis is where such a claim would be substantiated, discussed on our page on the peptide certificate of analysis.
One molecule, two freeze-dried formulations
Tesamorelin (PubChem CID 16137828; C221H366N72O67S, 5136 g/mol) is useful here because the same peptide is marketed in two FDA-labeled lyophilized formulations, and they differ in almost everything except the molecule.
| Property | EGRIFTA SV | EGRIFTA WR |
|---|---|---|
| Peptide per vial | Tesamorelin 2 mg | Tesamorelin 11.6 mg |
| Inactive ingredients | Mannitol, sucrose, histidine, polysorbate 20 | Hydroxypropyl betadex, mannitol |
| Labeled diluent | Sterile Water for Injection | Bacteriostatic Water for Injection, USP |
| Mixing motion, per label | Roll gently for 30 seconds; do not shake | Swirl in a circle; do not shake |
| Peptide share of solids | 6.1% | 5.8% |
Two points follow from this pair, and both contradict things that get said about freeze-dried peptides in general. First, the diluent is a property of the formulation, not of the molecule: one tesamorelin product is labeled with unpreserved sterile water and the other with preserved bacteriostatic water. Second, neither label permits shaking, and each prescribes a different gentle motion. Both labels also direct that the reconstituted vial be inspected visually for particulate matter and discoloration before use — the dissolved solution, not the dry cake, is what gets inspected.
Why freeze-drying, rather than drying with heat
A peptide is a chain held together by amide bonds, and water is the medium in which the reactions that break that chain proceed. Drying with heat would push those reactions faster on the way out. Freeze-drying avoids both problems at once: the material is frozen, the pressure is lowered, and the ice passes directly to vapour without ever becoming liquid, so the molecule is never warm and never sits in water at the end.
The payoff is measured in shelf life rather than in anything visible. GenScript’s published peptide storage and handling guidelines state that “the shelf-life of peptides in solution is very limited, much shorter than that of lyophilized peptides”, and that “lyophilized peptides should be stored at -20℃, away from bright light”, where “most lyophilized peptides are stable for several years”. That is the trade the form makes: an extra step before use, in exchange for a storage life measured in years instead of weeks.
Handling a dry vial: the two points manufacturers stress
Published handling guidance from peptide manufacturers concentrates on moisture, and on two moments in particular.
- Let the vial reach room temperature before it is opened. GenScript lists “warm the peptide vial to room temperature before opening” as the first step of preparation. A cold vial opened into warm room air collects condensation, and the material inside is the wrong thing to add water to by accident.
- Some sequences pull water out of the air. The same guidance notes that peptides containing aspartate, glutamate, lysine, arginine or histidine are “prone to moisture absorption from the air, called deliquescence”, and should be kept in a desiccator in a tightly capped vial. Which residues a sequence contains is therefore a handling property, not only a chemical one.
- Repeated freezing and thawing is its own cost. GenScript recommends aliquoting, which “reduces the number of freeze-thaw cycles, and reduces the amount of air exposure to the peptide”.
What happens after reconstitution is a separate question with a less tidy answer, and labeling for one single molecule can contradict itself across two formulations. That is set out on how to store peptides.
How the name is verified
A vial label carries a name, and a name is checkable. The glucagon label above states a molecular weight of 3483 and the empirical formula C153H225N43O49S for a 29-amino-acid peptide. PubChem’s record for glucagon (CID 16132283) returns the same formula and a molecular weight of 3482.7. The two agree, which is what a name matching a molecule looks like.
The check matters because the freeze-dried form hides everything a liquid would show. A dry white cake looks the same whatever it is, and its appearance carries no information about identity, purity or the amount of peptide present. Those are documentation questions, not visual ones.
Common misconceptions
- “The vial looks almost empty, so I was shorted.” The visible volume is mostly bulking agent. In the three labeled products above the peptide is 2–6.1% of the solids.
- “Lyophilized is a grade or a quality mark.” It describes how the water was removed. It says nothing about purity or identity.
- “Freeze-dried and heat-dried get you to the same place.” Freeze-drying exists precisely to avoid the heat.
- “Any lyophilized peptide takes the same diluent.” Two FDA-labeled formulations of tesamorelin name different ones.
- “Shaking dissolves it faster.” Both tesamorelin labels direct that the vial is not shaken, and prescribe a gentle motion instead.
What Medibact supplies
Medibact stocks USP-grade bacteriostatic water produced in an FDA-registered U.S. facility, sold for research use only. Medibact does not sell any peptide or labeled product named on this page and is not affiliated with Theratechnologies or GenScript; their labeling and published guidance are cited because they state what a freeze-dried vial contains and how such material is handled. Nothing here describes how any product should be used.
Where this sits in the rest of the reference
FAQ
What is a lyophilized peptide?
A peptide that has been freeze-dried: the peptide is dissolved, frozen solid, and then the ice is removed as vapour under vacuum rather than melted. What is left in the vial is a dry solid — usually a white to off-white cake or powder — that is dissolved again in a diluent before use. FDA labeling for freeze-dried peptide products calls this a “lyophilized powder”.
Is all the powder in the vial the peptide?
No, and usually most of it is not. In three FDA-labeled lyophilized peptide products the peptide is between 2% and 6.1% of the solids in the vial; the rest is inactive ingredients — bulking agents, stabilisers and pH agents such as mannitol, sucrose, lactose or hydroxypropyl betadex. A 1 mg glucagon vial, for example, also contains 49 mg of lactose. The size of the cake you can see is set mainly by those ingredients, not by the peptide.
Why are peptides freeze-dried instead of sold as liquid?
Because a peptide lasts far longer dry. GenScript's peptide storage guidance states plainly that “the shelf-life of peptides in solution is very limited, much shorter than that of lyophilized peptides”, and that most lyophilized peptides are stable for several years stored at −20 °C away from bright light. Removing the water removes the medium in which the reactions that degrade a peptide take place.
What does lyophilized powder look like, and does the amount tell me anything?
FDA labeling describes the reconstituted and unreconstituted material as white to off-white. It can look like a firm cake at the bottom of the vial, a loose powder, or a thin film dusted up the glass wall. Because the visible volume is set mainly by the bulking agent, the amount you can see is not a measure of how much peptide is present, and two vials of the same nominal strength can look different if they were formulated differently.
Does a lyophilized peptide need to be refrigerated?
Dry and reconstituted material are different questions, and the dry form is the more forgiving of the two. GenScript recommends −20 °C, dark, for lyophilized peptides. What happens after reconstitution is set by the individual product, and labeling for one single molecule can give contradictory answers — covered in full on our page on how to store peptides.
Should the vial be warmed before opening?
GenScript's handling guidance puts “warm the peptide vial to room temperature before opening” as its first preparation step, and notes that peptides containing aspartate, glutamate, lysine, arginine or histidine are “prone to moisture absorption from the air, called deliquescence”. Opening a cold vial into warm room air invites condensation onto material that readily takes up water.
Is lyophilized the same as freeze-dried?
Yes. Lyophilization is the technical name for freeze-drying. Both describe removing water from a frozen material by sublimation — ice turning straight to vapour under reduced pressure — rather than by heating, which would damage the molecule.
Do two vials of the same peptide contain the same formulation?
Not necessarily, and the clearest evidence is a single molecule with two FDA-labeled freeze-dried formulations. Tesamorelin is sold as EGRIFTA SV, formulated with mannitol, sucrose, histidine and polysorbate 20 and labeled for reconstitution with Sterile Water for Injection, and as EGRIFTA WR, formulated with hydroxypropyl betadex and mannitol and labeled for reconstitution with Bacteriostatic Water for Injection, USP. Same peptide, different inactive ingredients, different labeled diluent.
What diluent is a lyophilized peptide dissolved in?
Where a labeled product exists, its own label names the diluent, and the two tesamorelin formulations above name different ones. Bacteriostatic Water for Injection, USP is sterile water containing 0.9% benzyl alcohol as a preservative, which is what makes its container multiple-dose. This page gives no instruction for the use of any material.
Is this medical advice?
No. This is research-material education drawn from published FDA labeling and published manufacturer handling guidance. It contains no dosing, route or frequency instruction. Medibact is not affiliated with Theratechnologies, GenScript or any other company named here; their documents are cited because they state what is in a freeze-dried vial and how such material is handled.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.