How to Calculate Peptide Dosage for Your Body Weight

Peptide dosing in the research community frequently relies on fixed doses — for example, "take 250mcg BPC-157 twice daily" — regardless of whether the person weighs 55kg or 110kg. While fixed dosing is simpler, it means that a 55kg woman is receiving twice the per-kilogram dose of a 110kg man, which could produce different effects, side effects, and outcomes.

The case for body weight-based dosing:

Pharmaceutical dosing for many drugs is calculated per kilogram of body weight (mg/kg or mcg/kg), and there are good reasons for this: - Drug distribution is affected by body mass and composition - Receptor density scales roughly with body size - Clearance rates correlate with body weight and lean mass - Therapeutic windows (the range between effective and toxic doses) may be narrower in smaller individuals

The challenge with peptides:

Most research peptides lack established human doses entirely. The doses used in the community are extrapolated from animal studies using allometric scaling — a mathematical method for converting doses between species based on body surface area. These calculations produce estimated human-equivalent doses, but they are approximations, not validated therapeutic doses.

The practical reality:

For licensed peptide medications like semaglutide and tirzepatide, dosing is standardised through clinical trials and does not typically require body weight calculations (dose titration is used instead). For research peptides like BPC-157, TB-500, and GH secretagogues, body weight-based dosing is a more rational approach than one-size-fits-all fixed doses, even though the underlying dose-response relationships are poorly characterised.

This guide provides the mathematical tools to calculate body weight-based doses and accurately measure them from reconstituted peptide solutions. Getting the maths right is essential — dosing errors can result in either subtherapeutic doses (wasting money) or excessive doses (increasing risk).

Before any dosing calculation, you must be fluent in the unit conversions that underpin peptide measurement. Confusion between units is one of the most common and potentially dangerous errors in peptide research.

Mass units: - 1 milligram (mg) = 1,000 micrograms (mcg or μg) - 1 microgram (mcg) = 0.001 milligrams (mg) - Peptide vials are typically labelled in milligrams (e.g. "BPC-157 5mg") - Doses are typically discussed in micrograms (e.g. "250mcg twice daily")

Volume units: - 1 millilitre (ml) = 1 cubic centimetre (cc) - Insulin syringes may be marked in units (IU) rather than ml: 100 units = 1ml on a standard U-100 insulin syringe - 10 units on an insulin syringe = 0.1ml

Concentration after reconstitution: When you add bacteriostatic water to a lyophilised peptide vial, you create a solution with a specific concentration. This concentration determines how much liquid you need to draw to get your desired dose.

The key formula: Concentration = Total peptide in vial / Volume of water added

Example: - Vial contains 5mg BPC-157 (= 5,000mcg) - You add 2ml of bacteriostatic water - Concentration = 5,000mcg / 2ml = 2,500mcg per ml - On an insulin syringe (100 units = 1ml): each unit = 25mcg

Common reconstitution volumes and resulting concentrations (for a 5mg vial):

• •1ml water: 5,000mcg/ml (50mcg per unit on insulin syringe) — very concentrated, hard to measure small doses
• •2ml water: 2,500mcg/ml (25mcg per unit) — common choice, good balance
• •2.5ml water: 2,000mcg/ml (20mcg per unit) — easy maths for dose calculation
• •5ml water: 1,000mcg/ml (10mcg per unit) — dilute, requires larger injection volumes

The reconstitution choice affects your measurement precision. Using too little water creates a very concentrated solution where tiny measurement errors translate to large dose errors. Using too much water means larger injection volumes, which can be uncomfortable. Most researchers find 2–2.5ml to be optimal for a 5mg vial.

Most peptide dose recommendations in the community ultimately derive from animal studies. Understanding how these doses are converted provides important context for assessing their reliability.

The FDA allometric scaling method:

The US FDA provides guidance for converting animal doses to human equivalent doses (HED) using body surface area (BSA) correction factors. This is considered more accurate than simple weight-based scaling because metabolic rate scales with BSA rather than body weight.

The basic formula: HED (mg/kg) = Animal dose (mg/kg) x (Animal Km / Human Km)

Where Km is a correction factor: - Mouse Km = 3 - Rat Km = 6 - Human Km = 37

Example with BPC-157: - Many rat studies use 10mcg/kg BPC-157 - HED = 10mcg/kg x (6/37) = 1.62mcg/kg - For a 75kg human: 1.62 x 75 = 121.5mcg

This is notably lower than the 250–500mcg doses commonly used in the community. The discrepancy arises because: 1. Some community doses are based on different (higher) animal dose studies 2. Bioavailability differences between routes of administration may justify higher doses 3. There is no human data to validate any dose, so community doses have evolved through trial-and-error anecdotal experience 4. There is a natural tendency to escalate doses when effects are not immediately apparent

Important limitations of allometric scaling:

• •It is an estimation method, not a precise prediction
• •It assumes similar pharmacokinetics across species, which is often not the case
• •Route of administration matters: subcutaneous absorption may differ between rats and humans
• •Receptor density and sensitivity may differ between species
• •The method is designed to estimate a starting dose for Phase 1 clinical trials, not to determine a therapeutic dose

Body weight-based dose calculation for a specific peptide:

If a community protocol suggests 3mcg/kg/day of BPC-157: - 60kg person: 180mcg/day - 75kg person: 225mcg/day - 90kg person: 270mcg/day - 105kg person: 315mcg/day

This produces a more proportional dosing approach than a flat 250mcg for everyone.

Let us walk through a complete dosing calculation from start to finish, using realistic numbers.

Scenario: You weigh 70kg and want to calculate a BPC-157 dose of 3mcg/kg/day, split into two daily injections. You have a 5mg (5,000mcg) vial.

Step 1: Calculate your daily dose - Daily dose = body weight x dose per kg - Daily dose = 70kg x 3mcg/kg = 210mcg

Step 2: Calculate per-injection dose - Two injections per day: 210mcg / 2 = 105mcg per injection

Step 3: Choose reconstitution volume - Vial: 5mg = 5,000mcg - Choose 2ml of bacteriostatic water for easy maths and good precision - Concentration = 5,000mcg / 2ml = 2,500mcg per ml

Step 4: Calculate injection volume - You need 105mcg per injection - Volume = desired dose / concentration = 105mcg / 2,500mcg per ml = 0.042ml

Step 5: Convert to insulin syringe units - 0.042ml x 100 units per ml = 4.2 units on a U-100 insulin syringe - In practice, you would draw to the 4-unit mark (rounding down slightly for safety)

Step 6: Calculate how long the vial will last - Total peptide: 5,000mcg - Daily usage: 210mcg - Days per vial: 5,000 / 210 = approximately 23.8 days - Practical answer: approximately 23 days (accounting for loss during reconstitution and drawing)

Step 7: Verify with the volume check - Total volume: 2ml - Volume per injection: 0.042ml - Injections per vial: 2ml / 0.042ml = approximately 47.6 injections - At 2 injections per day: 23.8 days — consistent with the dose-based calculation

Common mistakes to avoid: 1. Confusing mg with mcg (1,000x error) 2. Forgetting to account for the reconstitution volume when calculating concentration 3. Using the wrong insulin syringe scale (U-40 vs U-100) 4. Not accounting for dead space in the syringe (approximately 0.05ml loss per injection with standard syringes) 5. Reconstituting with too little water, making precise small-dose measurement impossible

Even with perfect calculations, the accuracy of your dose depends on your ability to measure it precisely with a syringe. Understanding measurement precision is critical.

Insulin syringe precision:

• •1ml (100-unit) syringe: Each graduation mark represents 2 units (0.02ml). The smallest reliably measurable volume is approximately 2–3 units. This means your minimum measurable dose precision is about 50–75mcg with a 2,500mcg/ml solution.
• •0.5ml (50-unit) syringe: Each graduation mark represents 1 unit (0.01ml). Better precision for small doses — the minimum reliably measurable volume is about 1–2 units, or 25–50mcg with a 2,500mcg/ml solution.
• •0.3ml (30-unit) syringe: Each graduation mark represents 0.5 units (0.005ml). Best precision for very small doses.

Practical recommendation: For most peptide protocols, a 0.5ml (50-unit) insulin syringe with 1-unit graduations provides the best balance of precision and usability. The 0.3ml syringes offer better precision but are harder to read and less widely available in the UK.

Tips for accurate measurement:

1. Read at eye level. Hold the syringe at eye level with the markings facing you. Parallax error (viewing from an angle) can cause misreading. 2. Use good lighting. Measure in well-lit conditions where you can clearly see the graduation marks and the liquid meniscus. 3. Draw slowly. Pull the plunger back slowly and steadily to allow accurate filling without air bubbles. 4. Remove air bubbles. Tap the syringe gently with a fingernail, then push the plunger up to expel any air. Redraw to the correct mark. 5. Account for dead space. Standard insulin syringes have approximately 0.05ml of dead space (liquid that remains in the hub after the plunger is fully depressed). Low dead-space syringes are available but more expensive.

When precision matters most: For potent peptides where the dose is very small (less than 5 units on the syringe), consider reconstituting with more water to create a more dilute solution. This means drawing a larger volume, which is easier to measure precisely. The trade-off is a slightly larger injection volume.

Example: If your dose is 2 units from a 2ml reconstitution, reconstituting with 4ml instead would double the volume you need to draw (4 units), making measurement twice as precise with the same syringe.

The following tables provide body weight-adjusted doses for commonly researched peptides. These are based on community protocols and allometric scaling estimates — not validated human therapeutic doses. Use them as a starting reference, not as medical prescriptions.

BPC-157 (commonly cited range: 2–5mcg/kg/day):

Conservative approach (2.5mcg/kg/day): - 55kg: 137mcg/day - 65kg: 162mcg/day - 75kg: 187mcg/day - 85kg: 212mcg/day - 95kg: 237mcg/day - 105kg: 262mcg/day

Standard approach (3.5mcg/kg/day): - 55kg: 192mcg/day - 65kg: 227mcg/day - 75kg: 262mcg/day - 85kg: 297mcg/day - 95kg: 332mcg/day - 105kg: 367mcg/day

TB-500 (commonly cited range: 25–75mcg/kg, 2–3 times per week):

• •55kg: 1.4–4.1mg per dose, 2–3x weekly
• •75kg: 1.9–5.6mg per dose, 2–3x weekly
• •95kg: 2.4–7.1mg per dose, 2–3x weekly

Ipamorelin (commonly cited range: 1–3mcg/kg per dose):

• •55kg: 55–165mcg per dose
• •75kg: 75–225mcg per dose
• •95kg: 95–285mcg per dose

Important notes: 1. These are community-derived dose ranges, not medically established doses 2. Always start at the lower end of any range 3. Licensed medications (semaglutide, tirzepatide) have established dose titration schedules — follow those, not body weight calculations 4. Individual variation in response is significant — two people at the same weight may respond very differently 5. More is not necessarily better — some peptides show diminishing returns or increased side effects at higher doses 6. Consult a healthcare professional before using any peptide

*This calculator guide is for educational purposes only. It does not constitute dosing advice or medical recommendations. Peptide doses have not been validated in human clinical trials.*