The most common mistake in peptide therapy isn't picking the wrong compound. It's starting without baseline labs. Without a starting measurement, you can't know whether the peptide changed anything, whether your body responded as expected, or whether a symptom that appears during the protocol was pre-existing or peptide-related.
This guide covers the labs worth running at each stage. Not every test applies to every peptide — the panel depends on what you're taking.
Before you start: the baseline panel
These tests establish your metabolic, hormonal, and inflammatory starting point. Request them from your primary care provider or order directly through a consumer lab service.
For everyone starting any peptide protocol
Comprehensive Metabolic Panel (CMP): Kidney function (BUN, creatinine), liver function (ALT, AST), electrolytes, glucose. This is your safety baseline. If kidney or liver function is compromised, some peptides may not be appropriate.
Complete Blood Count (CBC): White blood cells, red blood cells, hemoglobin, platelets. Establishes your immune and hematologic baseline. Also catches iron-deficiency anemia — common in premenopausal women and a cause of fatigue that no peptide will fix.
Thyroid Panel (TSH, free T3, free T4): Thyroid dysfunction mimics many of the symptoms peptide users are trying to address — fatigue, weight gain, hair loss, brain fog. Rule it out before attributing these symptoms to GH deficiency or peptide candidacy.
Fasting Insulin and Glucose: Insulin resistance is relevant to GLP-1 peptide use, PCOS evaluation, and metabolic health broadly. Fasting insulin is the more sensitive marker — glucose can remain normal while insulin is already elevated.
Lipid Panel: Total cholesterol, LDL, HDL, triglycerides. GH influences lipid metabolism. Baseline values let you track whether GH secretagogues are affecting your lipid profile positively or negatively.
hs-CRP (high-sensitivity C-reactive protein): A marker of systemic inflammation. Relevant if you're using anti-inflammatory peptides (BPC-157, KPV) and want to track whether inflammation is actually changing.
For GH secretagogue protocols specifically
IGF-1 (Insulin-like Growth Factor 1): The primary biomarker for growth hormone activity. Your pituitary releases GH in pulses that are difficult to measure directly (GH has a half-life of minutes). IGF-1 is produced by the liver in response to GH and has a much longer half-life, making it a stable surrogate marker. Baseline IGF-1 establishes your pre-treatment GH axis status. Target ranges are age- and sex-specific — your provider should use female reference ranges.
Fasting glucose (repeated): GH antagonizes insulin — it can raise blood sugar. Monitoring fasting glucose during GH secretagogue use catches early glucose dysregulation, which is especially relevant for women with PCOS or pre-existing insulin resistance.
For hormonal peptide protocols
Estradiol, progesterone, LH, FSH: If you're using kisspeptin or any peptide that influences the reproductive axis, baseline sex hormones are essential. Timing matters — premenopausal women should test on day 3 of the menstrual cycle for FSH/LH/estradiol and day 21 for progesterone.
DHEA-S and testosterone (total and free): Relevant for women with PCOS or those using peptides that may influence androgen levels.
During the protocol: monitoring labs
Not every test needs repeating every month. The monitoring panel is targeted to the specific compounds you're using.
IGF-1 at 4-6 weeks: For GH secretagogues. Confirms the compound is producing a measurable GH response. If IGF-1 hasn't risen, either the compound isn't working, the dose is insufficient, or the product quality is questionable. If IGF-1 has risen dramatically (above the age-specific reference range), the dose may be too high.
Fasting glucose and insulin at 8-12 weeks: For GH secretagogues and GLP-1 peptides. Monitors metabolic effects — GH can worsen insulin resistance in some individuals, while GLP-1 peptides should improve it.
hs-CRP at 8-12 weeks: For BPC-157, KPV, or other anti-inflammatory protocols. A declining hs-CRP suggests the anti-inflammatory effect is real and measurable, not just subjective.
Liver function (ALT, AST) at 8-12 weeks: Precautionary monitoring for any injectable protocol. Most peptides are not hepatotoxic, but baseline-to-follow-up comparison catches unexpected effects.
After cycling off: the reassessment panel
Repeat the full baseline panel 4-6 weeks after completing a protocol block or cycling off. This shows you three things:
What changed: Compare post-protocol values to baseline. Did IGF-1 rise and then return to baseline after cycling off? Did hs-CRP decrease and stay lower? Did fasting insulin improve?
What persisted: Some changes outlast the protocol (improved insulin sensitivity, reduced inflammation). Others revert quickly (IGF-1 returns to baseline within weeks of stopping GH secretagogues). Understanding what persists helps you decide whether to continue, cycle, or stop.
What needs attention: Occasionally, a post-protocol panel reveals something unexpected — elevated liver enzymes, glucose dysregulation, or hormonal shifts. Catching these early is the value of systematic monitoring.
Labs your provider should not skip
If a clinician prescribes peptides without baseline labs, that's a yellow flag. If they prescribe GH secretagogues without checking IGF-1, that's a red flag. If they prescribe anything injectable without a metabolic panel, that's a provider who is selling product, not practicing medicine.
Labs are how you turn peptide therapy from a subjective experiment into a measured intervention. They're also how you protect yourself — both from compounds that aren't working and from compounds that are working too aggressively. The cost is modest relative to the peptide protocol itself. Budget for it from the beginning.