Dosing & Injection Basics

If you have your peptide reconstituted and you are ready for your first injection, this guide walks you through everything you need to know. We will cover how dosing actually works, how to read your syringe, where to inject, and how to do it with the least pain and the least risk.

If you have not yet reconstituted your peptide, start with our how to reconstitute peptides guide first. This page assumes you already have a properly mixed vial in your refrigerator.

Dosing Basics: The Core Concepts

Before you ever pick up a syringe, you need to understand four things about your peptide.

1. Total amount in the vial (mg)

This is printed on the label. For example, a “BPC-157 10 mg” vial contains 10 milligrams of BPC-157 in total. That total is divided across all the doses you will draw from the vial over its useful life.

2. Total water added (ml)

This is the amount of bacteriostatic water you added during reconstitution. For most products in our catalog, this is 2 ml, but it varies — see our reconstitution guide for product-specific recommendations.

3. Final concentration (mg/ml or mcg/ml)

This is how much peptide is in each millilitre of liquid in the vial. You calculate it with a simple division:

4. Desired dose

This is how much peptide you actually want to deliver per injection. Research dosing ranges vary widely between peptides — covered in the next section.

Once you know all four numbers, the math to calculate your injection volume is straightforward, and so is reading it on the syringe.

Reading an Insulin Syringe

Almost all peptide injections use what is called a U-100 insulin syringe. Understanding what the markings mean will save you from a lot of confusion.

• A standard U-100 insulin syringe holds 1 ml total and is marked with 100 units
• 100 units = 1 ml
• 10 units = 0.1 ml
• 1 unit = 0.01 ml

That ratio never changes. So when someone tells you to “draw 20 units,” they really mean “draw 0.2 ml.” The units are just a more practical way to read small volumes on the tiny markings of an insulin syringe.

Converting your dose into syringe units

Once you know your concentration, the formula to convert a dose into syringe units is:

If math is not your strong suit, do not worry — for every product in our catalog, the per-unit dose is listed in our reconstitution guide, so you can simply look up “each unit equals X mcg” and divide your target dose by that number.

A quick worked example

You have a BPC-157 10 mg vial reconstituted with 2 ml of BAC water (concentration: 5,000 mcg/ml). You want to dose 250 mcg.

• 250 mcg ÷ 5,000 mcg/ml = 0.05 ml
• 0.05 ml × 100 = 5 units on your insulin syringe

That is it. Draw to the 5-unit mark and you have 250 mcg ready to inject.

General Dosing Ranges (for Reference Only)

The table below shows the dosing ranges most commonly discussed in published research and protocol literature for peptides in our catalog. These are general informational ranges, not medical recommendations. The right dose for any individual depends on factors a healthcare professional can assess, including age, body composition, health status, and the specific goals of the protocol.

Healing & Recovery

Metabolic & Weight Loss

Growth Hormone Support

Longevity, Cognitive & Specialty

Frequency & Timing

How often you inject a peptide depends mostly on its half-life — the amount of time it takes for the peptide to drop to half its concentration in your bloodstream.

Short half-life peptides

Peptides like Sermorelin, Selank, and BPC-157 have relatively short half-lives, measured in hours. They are typically dosed once or twice daily to maintain steady levels.

Long half-life peptides

Peptides like CJC-1295 with DAC and Retatrutide have been engineered to last much longer in the body — days rather than hours. These are typically dosed once weekly.

Timing considerations

• Growth hormone-related peptides (Sermorelin, Tesamorelin, CJC) are often injected before bed because your body’s natural growth hormone release peaks during sleep, and you want the peptide to support that natural pulse rather than fight against it.
• Healing peptides (BPC-157, TB-4) are generally not time-dependent. Consistency matters more than time of day. Pick a time that works with your routine and stick to it.
• Metabolic peptides like Retatrutide are typically taken on the same day each week. Many users choose a day where mild nausea (a common early side effect) will not interfere with work or important plans.
• Sleep peptides (DSIP) are taken shortly before bed.
• NAD+ is often taken in the morning since some users report energy effects that can interfere with sleep if injected too late in the day.

Subcutaneous vs Intramuscular Injection

There are two main ways to inject a peptide. Knowing the difference matters because it changes which needle you use, where you inject, and how the peptide is absorbed.

Subcutaneous (SubQ)

Subcutaneous means “under the skin.” A SubQ injection delivers the peptide into the fatty tissue layer just beneath your skin, not into the muscle below it. This is the standard route for almost every peptide we sell.

Why SubQ is preferred for most peptides:

• Slower, more sustained absorption — better for peptides with longer effects
• Less painful — the fatty layer has fewer nerve endings than muscle
• Lower risk — much less chance of hitting a blood vessel or major nerve
• Easier to do yourself — shorter needle, gentler angle, more forgiving
• More injection site options across the body

Intramuscular (IM)

Intramuscular means “into the muscle.” IM injections use longer needles to push past the fat layer and into the muscle tissue itself. Absorption is faster.

IM injection is rarely used for the peptides we sell. It is sometimes mentioned in research protocols for specific peptides where faster absorption is desired, but for most of our products, subcutaneous is the standard route. If you read a protocol calling for IM injection, double-check that the source is reliable and consult a healthcare professional before changing routes.

Supplies You’ll Need for Injection

Have these ready before you take the vial out of the refrigerator:

• Insulin syringes — U-100, 29 to 31 gauge, with a 1/2 inch (12.7 mm) needle. The thinner the gauge number, the thicker the needle. 31 gauge is the thinnest and least painful. Use a fresh syringe for every injection — never reuse.
• Alcohol swabs — 70% isopropyl prep pads. You need at least two per injection: one for the vial stopper and one for your injection site.
• Sharps container — a puncture-resistant container for safe needle disposal. Never put used needles in regular trash. Many pharmacies in Costa Rica can provide one or accept used ones.
• Cotton ball or gauze — for very minor bleeding after injection (rare, but useful to have).
• A clean, well-lit workspace — a kitchen counter or desk works well. Avoid the bathroom (humidity).

Choosing the right syringe size

Insulin syringes come in three common sizes. The right one depends on how big your typical dose is:

Smaller syringes have larger, more readable unit markings, which can be helpful when measuring small doses. For most peptide users, a 0.5 ml syringe is the right default.

Best Injection Sites for SubQ Injections

You have several good options for where to inject. Rotating between sites is important because injecting the same spot every time can cause irritation, lumps under the skin, or changes in fat tissue over time.

How to rotate sites

The simplest rotation pattern is to mentally divide each injection area into a grid of 4 to 8 spots, and move to a different spot for every injection. Many users keep a simple notebook or phone note tracking the site of each injection so they don’t accidentally repeat. Avoid injecting into any spot showing bruising, redness, broken skin, scars, tattoos, or visible blood vessels.

The Injection Itself: Step by Step

Here is the full process from start to finish. Read through this once before your first injection so nothing surprises you.

What to Expect After Your Injection

Most subcutaneous peptide injections are remarkably uncomfortable-free. Most users describe the sensation as similar to or less than a mosquito bite.

Things that are normal

• Mild redness or a small bump at the injection site for a few hours
• A tiny droplet of blood when you remove the needle
• Slight stinging during the injection itself, especially in leaner areas
• A small bruise occasionally if the needle nicked a tiny capillary

Things that warrant attention

• Significant swelling, spreading redness, or warmth at the injection site that worsens over 24 hours
• Itching, hives, or rash beyond the injection site
• Difficulty breathing, swelling of the face or throat, or dizziness — these are signs of a possible allergic reaction and require immediate medical attention
• Persistent lumps or hardened tissue at injection sites used repeatedly — usually means you need to rotate sites more aggressively

If anything seems unusual or concerning, contact a qualified healthcare professional. Trust your instincts — if something feels off, get it checked.

Common Mistakes to Avoid

Injecting cold peptide

The single easiest way to make an injection hurt more than it needs to. Always let the vial warm up to room temperature first.

Not letting the alcohol dry

Injecting through wet alcohol stings unnecessarily. Let it air dry for 15 seconds before piercing the skin.

Injecting in the same spot repeatedly

Daily injections in the same area cause irritation, scarring, and changes in fat tissue. Rotate consistently.

Reusing needles

A used needle is duller and may be contaminated. Even for the same vial, the same day, the same person — always use a fresh syringe per injection.

Recapping needles after use

Most accidental needle sticks happen during recapping. Drop used needles directly into a sharps container without trying to recap.

Drawing your dose hours in advance

Pre-loading a syringe and letting it sit increases contamination risk and may degrade the peptide. Draw your dose right before injection.

Pushing too hard or too fast

Injecting too quickly causes stinging and can trap small bubbles under the skin. Steady, smooth pressure over 2–3 seconds is ideal.

Going too high on the abdomen

Avoid the area within 2 inches of your navel — the tissue there is thinner and more sensitive. Stay in the broader belly area below or to the side.

Common Questions

Important disclaimer: The information in this guide is general educational content only. It is not medical advice, a prescription, or a personalized dosing recommendation. Dosing ranges mentioned reflect what is commonly discussed in published research and protocol literature; they are not endorsements of those doses for any specific individual. Peptide use should always be undertaken in consultation with a qualified healthcare professional who can evaluate your medical history, current health status, and goals. Products sold by Peptides Costa Rica are intended for laboratory and research purposes only.