“Peptide stack” is a phrase people search for a lot. It is not a medical term. This page explains what the two words mean, and how STACK, the app, handles a plan that includes more than one compound.

What a peptide is

A peptide is a short chain of amino acids. Where the line sits between “peptide” and “protein” is a matter of convention, and the FDA settled it for regulatory purposes in 2020: a protein is “any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size,” and the agency notes that the term “peptide” generally refers to the smaller, simpler chains [1]. Insulin, at 51 amino acids across two chains, counts as a protein under that rule [1].

Peptides have been medicines for a century. More than 80 peptide drugs have reached the market since insulin, across diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain [2]. Over 150 more were in active clinical development as of 2017 [3]. The GLP-1 drugs are peptides: semaglutide’s label describes a “peptide backbone” made by yeast fermentation and then chemically modified so it binds albumin and resists breakdown [4].

What people mean by a stack

“Stack” is borrowed from fitness and supplement slang. It just means using more than one compound in the same plan. That is all it means. It does not imply the compounds were studied together, that they are safe together, or that there is a right combination.

You will see the phrase “cjc 1295 ipamorelin” in search a lot, because those two names are often written together. Both appear on the FDA’s list of bulk substances that may present significant safety risks for compounding, where the agency cites limited clinical data for CJC-1295 and serious adverse events reported with intravenous ipamorelin [7]. This page does not describe what either does, and STACK does not suggest any combination. If you are using two or more compounds, that decision belongs to your prescriber, in writing, with an evaluation behind it.

Why STACK tracks each compound separately

Two compounds in one plan are still two different drugs. They differ in ways that matter for tracking:

Half-life. Semaglutide’s elimination half-life is about 1 week, and the label says it stays in circulation for roughly 5 weeks after the last dose [4]. Liraglutide’s is about 13 hours [5]. Those two curves look nothing alike, and a single blended curve would be meaningless.
Units. Approved GLP-1 products are labeled in milligrams [4][5][6]. Other compounds are written in micrograms or international units. STACK stores the unit with each entry as the prescriber wrote it, and never converts between compounds.
Schedule. One compound may be weekly, another daily. STACK keeps a separate schedule per compound, so a missed or shifted dose is flagged for the right one.
Sites. The Zepbound Medication Guide tells patients to rotate injection sites and not reuse the same site each time [6]. When two compounds are injected, STACK logs the site for each so rotation is tracked for each compound, not just by date.

Because of these differences, STACK shows separate estimated level curves, one per compound, on a shared timeline. You can view them together to see how they overlap, but each is calculated on its own from its own published half-life, and each is an estimate, not a blood level.

What STACK does not do

STACK does not recommend compounds, combinations, amounts, timing or how long to continue. It has no “best peptides” list. It will not fill in a schedule you have not entered. If a compound has no published human half-life, STACK says so and lets you enter your own estimate, clearly labeled as yours.

Compounded drugs, including compounded peptides, are not FDA-approved, which means the FDA has not verified their safety, effectiveness or quality before they are sold [8]. That does not change how STACK tracks them, but it does mean the label from your pharmacy, and your prescriber’s instructions, are the only authority on what you were given.

When to talk to your prescriber

Call your prescriber before adding, removing or changing any compound in your plan. If a symptom appears after a second compound is added, STACK’s side-effect log shows it on the timeline next to both compounds’ doses so you can share the picture rather than a guess.

Free tools

Sources

Every URL below was fetched and checked on 2026-09-24. Bracketed numbers in the text link here.

What is a peptide stack?