Peptides can sound complicated, but the core ideas are simple. This guide walks you through them in the order you will need them, from what a peptide actually is to reading a syringe. Each step links to a deeper guide when you are ready for more.
Educational information only. Nothing here is medical advice. Talk to a qualified healthcare professional before starting, stopping or changing anything.
1. What is a peptide?
A peptide is a short chain of amino acids, the same building blocks that make up proteins. A helpful way to picture it: amino acids are letters, peptides are short messages, and proteins are long instructions.
Your body already makes thousands of peptides. Many work as signals: they attach to a receptor on a cell and tell that cell to do something, such as release a hormone, repair tissue or reduce appetite. Insulin is a well-known example.
How peptides differ from other things you may have heard of:
- Proteins are longer chains (usually 50+ amino acids) with more complex shapes.
- Steroids are a completely different chemical family built on a ring structure, not amino acids.
- Supplements such as collagen peptides are digested as food. Most signalling peptides are broken down in the stomach, which is why many are injected instead.
2. Reading the research
Information about peptides comes from three places: human studies, animal studies and the experience of people who use them. Throughout this site we note which one a statement is based on, so you can weigh it for yourself. Human studies are the strongest guide, animal studies show early promise, and user reports fill in the practical details.
3. The supplies, and what each one is for
- Peptide vial: usually a small glass vial with a freeze-dried (lyophilized) powder, sometimes called a “puck.” The label shows the total amount, such as 5 mg or 10 mg.
- Bacteriostatic water (BAC water): sterile water with 0.9% benzyl alcohol, a preservative that slows bacterial growth so a mixed vial can be used more than once.
- Insulin syringes: small syringes marked in “units.” Common sizes are 0.3 mL (30 units), 0.5 mL (50 units) and 1 mL (100 units).
- Alcohol swabs: to clean vial stoppers and the skin.
- Sharps container: a puncture-proof container for used needles. Never throw loose needles in household trash.
4. Units explained: mg, mcg, mL and syringe units
This is where most beginner mistakes happen, so it is worth slowing down.
| Unit | What it measures | Key fact |
|---|---|---|
| mg (milligram) | Amount of peptide | 1 mg = 1,000 mcg |
| mcg (microgram) | Amount of peptide | 250 mcg = 0.25 mg |
| mL (milliliter) | Volume of liquid | 1 mL = 100 syringe units |
| Unit (U-100 syringe) | Volume marking on the syringe | 1 unit = 0.01 mL |
The important idea: syringe units measure liquid, not peptide. How much peptide is in each unit depends on how much water you mixed into the vial. That is why you can never copy someone else’s “units” unless your vial size and water amount match theirs exactly.
Watch out for U-40 syringes. Some veterinary syringes use a different scale. Every calculation on this site assumes standard U-100 insulin syringes.
5. Reconstitution: mixing the vial
“Reconstitution” just means adding liquid to the powder so it can be measured. The basic steps:
- Wash your hands and clean your work surface.
- Wipe the rubber stoppers of the peptide vial and the BAC water vial with an alcohol swab and let them dry.
- Draw the planned amount of BAC water into a syringe.
- Insert the needle into the peptide vial and let the water run slowly down the inside wall of the glass, not directly onto the powder.
- Gently swirl or roll the vial until the powder dissolves. Do not shake it.
- Label the vial with the date and the concentration, then refrigerate it.
The solution should be clear. If it is cloudy, discolored or has particles, do not use it. The full Reconstitution Guide covers each step in more detail, with troubleshooting.
6. Using the calculator
Once a vial is mixed, you need to know how many units to draw for your dose. Our Peptide Calculator asks for three numbers:
- The amount of peptide in the vial (mg)
- The amount of water you added (mL)
- Your dose (mcg or mg)
Worked example: a 5 mg vial mixed with 2 mL of water has a concentration of 2.5 mg/mL (2,500 mcg/mL). A 250 mcg dose is 250 ÷ 2,500 = 0.1 mL, which is the 10 unit mark on a U-100 syringe. That vial holds 20 doses of that size.
The calculator does arithmetic only. It does not tell you what dose is right for you.
7. Ways peptides are taken
- Subcutaneous injection: into the fat just under the skin, most often the belly, upper thigh or back of the arm. This is the most common route.
- Intramuscular injection: into a muscle. Used for some peptides.
- Nasal spray: used for several brain-focused peptides, such as Semax and Selank.
Rotate injection sites so the same spot is not used repeatedly. Each encyclopedia entry lists the routes that apply to that peptide.
8. Storage
- Before mixing: keep vials cool, dry and away from light. Many are stored in the refrigerator or freezer for longer life.
- After mixing: keep the vial in the refrigerator (about 2–8 °C / 36–46 °F), upright and away from light. Do not freeze mixed vials.
- How long a mixed vial lasts varies by peptide. Check the storage section of each encyclopedia entry.
9. Side effects and red flags
Common, usually mild effects include redness, itching or a small bump at the injection site. Some peptides have their own well-known side effects, such as nausea with GLP-1 peptides.
Stop and get medical help if you notice signs of an allergic reaction (swelling of the face or throat, trouble breathing, widespread hives), signs of infection at an injection site (spreading redness, heat, pus, fever), or any severe or unexpected symptom.
10. Cycling, titration and stacking
You will see these three words often:
- Titration: starting at a low dose and increasing slowly. GLP-1 peptides such as semaglutide and tirzepatide, for example, are always started this way to reduce side effects.
- Cycling: using a peptide for a period, then taking a break. For some peptides this is meant to keep the body responding.
- Stacking: using two or more peptides together because they are thought to work in complementary ways.
11. Quality and sourcing
Quality varies between suppliers. Two vials with the same label can contain different amounts, or the wrong substance. A certificate of analysis (COA) from an independent lab, matched to the batch number on your vial, is the minimum check. See our guide to reading a COA.
Where to go next
- Browse the Peptide Encyclopedia
- Try the Peptide Calculator
- Look up a term in the Glossary