How to measure peptide outcomes

Why this guide exists

Peptides are powerful enough to make the subjective story ("I feel sharper," "I'm recovering faster") feel true regardless of what the molecule is actually doing. Without a feedback loop, you can't distinguish a real effect from placebo, and you can't separate a benefit vector from a side-effect vector.

This guide is the practical companion to the "Everyone's injecting peptides, almost no one is measuring them" explainer. The explainer makes the case; this guide tells you exactly which test to order, from which service, at what cost.

It is not medical advice. It is a measurement framework. Discuss specific protocols with a qualified clinician.

The four measurement layers

A full outcome-measurement stack has four layers:

1. Baseline bloodwork — before dose 1.
2. Continuous glucose — a 14-day CGM window during the protocol.
3. Autonomic and sleep wearables — 24/7, ideally starting 2 weeks before dose 1 to establish a baseline.
4. Structured training and subjective logs — daily, throughout.

You can run the whole stack for roughly £300–500 per 8-week protocol in the UK, less in the US if you already have a wearable.

Layer 1 — baseline bloodwork

What to order

Absolute minimum for any peptide protocol:

• Full blood count (FBC)
• Liver function (LFTs)
• Kidney function (U&Es)
• Full lipid panel including ApoB and Lp(a)
• Fasting glucose and insulin — calculate HOMA-IR
• HbA1c
• TSH, free T3, free T4
• Morning cortisol
• hsCRP

Additions by peptide class:

• GH secretagogues (CJC-1295, sermorelin, tesamorelin, ipamorelin, MK-677): add IGF-1 (critical — this is the primary read-out).
• GLP-1s (semaglutide, tirzepatide, retatrutide, orforglipron): add C-peptide, lipase, amylase.
• BPC-157 / TB-500: the minimum panel is enough.
• NAD+ precursors: add methylation panel (homocysteine, B12, folate) if dosing high.

Where to order (UK)

• Medichecks — the most comprehensive at-home panel options. An "Advanced Well Man/Woman" plus IGF-1 add-on covers the minimum.
• Thriva — simpler at-home finger-prick, useful for light-touch retesting.
• Randox / London Medical Laboratory — more technically sophisticated if you want full CMP and hormone extensions.
• Private GP — any Spire, HCA, or independent GP will order the panel. Cost is higher; you get a clinician letter with it.

Typical UK cost: £90–180 for the minimum panel, £140–260 with IGF-1 and C-peptide extensions.

Where to order (US)

• Marek Health — peptide-aware, will also write prescriptions if needed.
• Function Health — batched annual panel, consumer-friendly interface.
• Quest Health / Labcorp OnDemand — direct-to-consumer, most affordable per-test.
• Primary care physician — insurance typically covers the minimum if there's a documented reason.

Typical US direct-to-consumer cost: $150–350 for the minimum panel, higher with hormone extensions.

Layer 2 — continuous glucose

Any GH secretagogue, GLP-1, or insulin-affecting stack benefits from a 14-day CGM window during weeks 2–4 of the protocol. Two options:

• Freestyle Libre 3 — at-home, no prescription required in most EU countries. In the UK, available direct-to-consumer from Abbott or via GP. Cost ~£60 per 14-day sensor.
• Dexcom G7 — similar, marginally better accuracy, prescription-required in most jurisdictions.

What to watch:

• Fasting glucose drift across the two weeks.
• Post-meal excursions (peak glucose 60–90 minutes after carbs).
• Overnight glucose (4 am glucose is often the cleanest endpoint).

A CGM during the protocol plus fasting glucose/insulin on the baseline panel catches the vast majority of metabolic side-effects from GH-secretagogue work before they show up on a repeat HbA1c.

Layer 3 — autonomic and sleep wearables

A wrist- or ring-worn wearable with a validated HRV signal running 24/7 gives you:

• Resting heart rate trend (the earliest signal to move on any GLP-1)
• HRV baseline and deviation (autonomic stress response)
• Sleep architecture: deep sleep, REM, latency, efficiency

Validated options:

• Oura Ring — best validated HRV and deep-sleep signal in the consumer segment.
• Whoop — strong HRV, subscription model, heavier on subjective recovery framing.
• Apple Watch + a strong third-party app (AutoSleep, Athlytic) — adequate if you already own one.
• Garmin — strong for athletes, less granular sleep tracking than Oura.

What to do:

1. Wear the device for at least 2 weeks before dose 1 to establish personal baseline ranges.
2. Log dose days vs off days if the protocol isn't daily.
3. Watch for 3+ day directional trends, not day-to-day noise.

Layer 4 — structured logs

The one thing no wearable or blood panel captures: subjective response and performance output.

A minimum log, daily, takes 60 seconds:

• Bodyweight — first thing, same scale, same conditions.
• Sleep hours + subjective quality (1–10).
• Workout volume — set/rep/weight if lifting; distance/pace if running.
• Energy and mood (1–10).
• Dose (peptide, amount, timing).
• Side effects (specific: nausea, HR spikes, joint water retention, appetite shifts).

A Notion template or a plain spreadsheet is enough. The point is that over 8 weeks you have a time series you can correlate against your bloodwork and wearable data.

Repeat cadence

For an 8-week protocol:

• Week 0: full baseline bloods + 2 weeks of wearable baseline.
• Week 2: start CGM. Stays on through week 4.
• Week 4: mid-protocol bloods — IGF-1 + fasting glucose/insulin + any class-specific markers.
• Week 8: full post-protocol bloods (same panel as week 0).

Weekly bloods at Bryan Johnson's cadence are achievable for self-funded adults but overkill for most first protocols. Every 4 weeks is a realistic floor.

The pre-protocol checklist

Before dose 1, answer these in writing:

1. What specific outcome am I trying to produce? (body composition, recovery, sleep, metabolic — pick one primary)
2. What biomarker or measurement will tell me whether it worked?
3. What side-effect vector am I most at risk of, and how will I catch it early?
4. What is my stop rule — the specific measurement change that would make me halt the protocol?

If you can't answer those four questions, don't start the protocol yet.

Where to go next

• Explainer: Everyone's injecting peptides, almost no one is measuring — the "why" behind this guide.
• Bryan Johnson's measurement stack — the maximalist version.
• How to evaluate a peptide vendor.
• How to buy your first peptide in the UK.