Is Tirzepatide a Peptide? And NAD+, Creatine, Glutathione, GLP-1, hCG and Enclomiphene

Tirzepatide is a peptide. NAD+ is not. Creatine is not. Glutathione is. GLP-1 is. hCG is not, on a technicality worth understanding. Enclomiphene is not, and it is not close. Those are the answers, and the rest of this page is the one rule they all come from, so the next compound you wonder about does not need a search.

The question keeps getting asked because "peptide" has stopped describing chemistry and started describing a shopping channel. A vendor's catalogue holds tirzepatide, NAD+, glutathione, 5-amino-1MQ and MK-677 in identical vials, reconstituted with the same bacteriostatic water and measured on the same syringe. Some are peptides and some are not. The vial tells you nothing.

The rule, and it is one rule

A peptide is a chain of two or more amino acids joined to each other by peptide bonds. A peptide bond is an amide bond: the carboxyl of one amino acid reacts with the amino group of the next, water comes off, and the two residues are linked through a carbon to nitrogen bond. Two residues is a dipeptide, three a tripeptide, more a polypeptide. That gives three questions, and which one a compound fails tells you what it is instead.

1. Is it built from amino acids at all? If not, it is not a peptide and never will be. NAD+ and enclomiphene fall out here. They are not unusual peptides; they are different classes of molecule entirely.
2. Are those amino acids joined to each other by peptide bonds, in a chain? Being made from amino acids is not the same as being made of them. Creatine fails here, and it is the most misunderstood point in the whole family of searches.
3. Is the chain roughly fifty residues or fewer? Above that, convention calls it a protein. This is the only question hCG fails, which is why the honest answer for hCG is "no, but".

The fifty residue line is the soft part. Nothing changes chemically at residue fifty-one. Some texts put the boundary at 100 residues, others at a molecular weight around 5 to 10 kilodaltons, and a structural criterion is often layered on top: proteins fold into a defined shape their function depends on, while most peptides are too short to hold one. Insulin shows how arbitrary it is. At 51 amino acids across two disulfide-linked chains it is one residue over, and the literature calls it a protein and a peptide hormone interchangeably.

The short answers

Is tirzepatide a peptide?

Yes, a synthetic peptide of 39 amino acids, in exactly the same sense that oxytocin and semaglutide are.

The backbone comes from native GIP, glucose-dependent insulinotropic polypeptide, which the gut secretes at 42 residues. Lilly's molecule keeps the part of that sequence that matters, engineers it to hit both the GIP and the GLP-1 receptor, and makes two changes worth knowing. Two positions carry alpha-aminoisobutyric acid, a non-standard residue DPP-4 cannot get a grip on, which is the countermeasure to the enzyme that destroys native GIP and GLP-1 within minutes. And a C20 fatty diacid is attached through a linker to a lysine side chain, which binds circulating albumin and stretches the half-life to roughly five days, allowing weekly dosing.

None of that stops it being a peptide. Non-standard residues and a fatty acid decoration are modifications to a chain, not a departure from one, and 39 residues is under the line by any version of the convention. Oral tirzepatide is still a peptide too: surviving the stomach is a formulation problem, not a change to the molecule. The tirzepatide dosage guide covers the 2.5 mg start and escalation, compounded tirzepatide where the supply comes from, and semaglutide vs tirzepatide the single-receptor option.

Is NAD a peptide?

No, and this is not a close call. NAD is nicotinamide adenine dinucleotide, and the name is the answer: a dinucleotide. It is two nucleotides, nicotinamide mononucleotide and adenosine monophosphate, joined through a pyrophosphate bridge. No amino acid in it, therefore no peptide bond in it, and at about 663 daltons it is a small molecule with entirely different architecture from a chain.

What it does is nothing like what a peptide does either. Peptides are signalling molecules that bind receptors at the cell surface. NAD+ is a coenzyme, an electron shuttle in hundreds of metabolic reactions and a substrate for the sirtuins and PARP enzymes, which is how it became a longevity compound. It works inside the cell's chemistry, not at its surface.

There is one real connection, and it is probably the root of the confusion: the body can build NAD from tryptophan, an amino acid, through the kynurenine pathway. A precursor relationship is not a structural one. Tryptophan is also the precursor to melatonin, and nobody asks whether melatonin is a peptide. The NAD+ injection dosage page covers the protocols in circulation.

Is NAD+ a peptide?

No. Same molecule, same answer, and the plus sign is the only thing that changes between the two searches.

Since a lot of people are really asking what the plus means: NAD cycles between two forms. NAD+ is the oxidised form, ready to accept a pair of electrons; NADH is the reduced form, carrying them. The plus records the positive charge on the nicotinamide ring nitrogen. It is standard redox notation, the same convention behind NADP+ and NADPH, and says nothing about size, class or amino acid content.

So if you have found NAD+ shelved between MOTS-c and PT-141, the shelf is wrong about taxonomy and right about everything else: same trade, same vial, same reconstitution arithmetic. Its neighbour MOTS-c is a genuine 16 amino acid peptide encoded in mitochondrial DNA. NAD+ is not a peptide at all.

Is creatine a peptide?

No. Creatine is methylguanidinoacetic acid, a single small molecule of about 131 daltons, with no peptide bond anywhere in it. This question deserves the most care, because the thing people half-remember is true and the conclusion they draw from it is wrong.

The true part: the body synthesises creatine using three amino acids, glycine, arginine and methionine. The wrong part is the inference that creatine is therefore those three joined together, a tripeptide. Look at what each one contributes.

Three amino acids contribute atoms, and not one ends up bonded to another by an amide bond. Only glycine's skeleton survives intact. Arginine leaves behind a functional group and departs as ornithine. Methionine contributes a single carbon. Calling that a tripeptide is like calling a cake a flour, because flour was involved.

The second source of confusion is commercial. "Creatine peptides" are a real product: creatine attached to short peptides, usually hydrolysed collagen, sold on an absorption claim. The peptide in that name is the collagen fragment, not the creatine. Creatine is also the only compound here that is a mainstream food supplement rather than a research chemical, with decades of human trials behind it. The peptide supplements page covers the wider category of things sold as peptides that are not.

Is glutathione a peptide?

Yes. Glutathione is a tripeptide: gamma-L-glutamyl-L-cysteinylglycine, three residues, about 307 daltons. It is probably the most important peptide in the human body that almost nobody thinks of as a peptide, because it is filed under antioxidants.

One of its two bonds is unusual, and the consequence is functional. In an ordinary peptide the chain runs through the alpha-carboxyl of each residue. In glutathione the glutamate attaches to the cysteine through its gamma-carboxyl, the one on the side chain, which makes that an isopeptide bond. Standard aminopeptidases cannot cleave it, which is why glutathione survives in the cytosol at millimolar concentrations and why the body needs gamma-glutamyl transpeptidase to break it down. The cysteine to glycine bond is a normal alpha peptide bond, so the molecule carries one of each.

Glutathione is also not made by the ribosome. Two dedicated enzymes assemble it, glutamate-cysteine ligase and then glutathione synthetase, each adding one residue. It is still a peptide, because being ribosomally translated is not part of the definition, and that matters: most research peptides in circulation are built off-ribosome too, one residue at a time on a resin. The working end is the cysteine thiol, oxidised to the disulfide-linked GSSG and recycled by glutathione reductase, and the vial reconstitutes like any other, which the reconstitution guide covers.

Amino Club lists glutathione in its research catalogue, and PSPeptides carries it too, the only vendor on the Bureau's scorecard that ships outside the US. Both links show the live price. Research use only, and links in this paragraph may earn the Bureau a commission.

Is GLP-1 a peptide?

Yes, and the name gives it away: glucagon-like peptide-1. It is a peptide hormone, and it is the parent of the entire drug class everyone is actually asking about.

The native hormone is cut out of proglucagon by prohormone convertase 1/3 in the L cells of the intestine. The two biologically active forms, GLP-1(7-36) amide and GLP-1(7-37), are 30 and 31 residues. Both are destroyed fast: DPP-4 clips the first two residues off the N-terminus and the circulating half-life is a minute or two, which is precisely the problem every GLP-1 drug exists to solve. The how semaglutide works page walks through the receptor biology.

Almost every GLP-1 receptor agonist in use is itself a peptide, and each is a different answer to the DPP-4 problem:

• Semaglutide, 31 residues, Aib at position 8 to block DPP-4 and a C18 diacid for albumin binding. A peptide. See the semaglutide dosage guide.
• Liraglutide, 31 residues, palmitic acid instead of the diacid, which buys a day rather than a week. A peptide.
• Exenatide, 39 residues, a synthetic copy of exendin-4 from Gila monster venom, which resists DPP-4 natively. A peptide, and not a GLP-1 analogue at all.
• Retatrutide, a triple GIP, GLP-1 and glucagon agonist. A peptide. See the retatrutide guide.
• Orforglipron, an orally active small molecule GLP-1 agonist. Not a peptide, and the exception that proves the class is not defined by chemistry.

So "is GLP-1 a peptide" is a yes, and "is every GLP-1 drug a peptide" is a no, with the small molecule agonists as the growing exception. Cagrilintide, often stacked alongside them, is a peptide too, but an amylin analogue rather than a GLP-1 one. The weight loss peptides page compares the class.

Is hCG a peptide?

No, by the size convention, and this is the one answer on the page that comes with an asterisk rather than a flat rejection.

Human chorionic gonadotropin is a glycoprotein hormone, and a heterodimer: an alpha subunit of 92 amino acids, shared with LH, FSH and TSH, and a beta subunit of 145 that makes it hCG rather than one of the others. The chains are held together non-covalently and both are heavily glycosylated. Total molecular weight is roughly 36 to 37 kilodaltons, of which about 30 percent is carbohydrate.

Run that against the rule. It passes questions one and two: built from amino acids, joined by ordinary peptide bonds into chains. It fails question three, and not marginally. Each chain alone is well over the fifty residue line and together they are nearly five times it. That makes hCG a glycoprotein, on the far side of a boundary tirzepatide is nowhere near.

The asterisk matters because it is a different kind of no from NAD+ or enclomiphene. hCG is the same chemistry as a peptide, just more of it, and behaves like a peptide hormone in every functional sense: made by the body, binds a cell surface receptor, destroyed if swallowed. Calling it a peptide hormone in conversation is loose but defensible. Calling NAD+ a peptide is simply wrong.

One practical note, because of the company it keeps. hCG is a prescription drug in the United States and is not carried by any vendor the Bureau scores. Anything sold as hCG through a research channel deserves the scepticism the fake vendor guide describes: a 36 kDa glycosylated heterodimer is far harder to make correctly than a 15 residue chain, and a generic purity certificate would not tell you whether it had been. The testing guide covers what a COA can and cannot establish.

Is enclomiphene a peptide?

No. Enclomiphene is a small molecule, and of everything on this page it is furthest from a peptide.

Chemically it is the trans isomer of clomiphene, a triphenylethylene: three benzene rings around a carbon to carbon double bond, about 406 daltons as the free base. No amino acids, no amide backbone, no chain of anything. Clomiphene citrate as prescribed is a mixture of two isomers, roughly 60 percent enclomiphene and 40 percent zuclomiphene, and separating out the enclomiphene is the whole premise of the standalone product, since zuclomiphene is the longer-lived and more estrogenic half.

It acts as a selective estrogen receptor modulator at the hypothalamus and pituitary. By blocking estrogen's negative feedback there it raises LH and FSH, which raises endogenous testosterone. That is why it sits next to peptides on the same shelf: the goal overlaps with kisspeptin analogues and with hCG. But a SERM and a peptide are unrelated classes aimed at the same axis from different directions.

The practical consequence is the useful part: enclomiphene is orally active and stable because there is no peptide bond for a protease to find. Chemistry determines route. If a compound is sold as a plain oral tablet with no absorption enhancer and no special handling, that is a strong hint it is not a peptide. For the peptide-side options aimed at the same goals, see peptides for erectile dysfunction and the PT-141 guide.

The near misses people ask about next

Two patterns. Metal ions, disulfide bridges, fatty acid chains and non-standard residues are modifications to peptides, not disqualifications: GHK-Cu carrying a copper ion is still a tripeptide, as the GHK-Cu guide sets out. And the compounds that genuinely are not peptides tend to declare themselves by working as plain tablets.

Why the classification actually matters

Route, handling and regulation all follow from chemistry. A peptide bond is a target for gut proteases, which is why peptides are almost always injected, shipped lyophilised and kept cold once reconstituted, while a small molecule has none of those constraints; the storage guide covers it. The regulatory line is drawn here too: the FDA's own peptide to protein cut at 40 amino acids decides whether something is regulated as a drug or a biologic, and governs what can be compounded and by whom, which is part of why the 2026 decisions on the PCAC vote page landed as they did.

What it does not tell you is what evidence to expect. Tirzepatide has phase 3 trials and an approval. BPC-157, a 15 residue fragment of a gastric protein, has a rodent literature and no published human trials. Both are peptides. Creatine, which is not one, has more human data behind it than most of the research peptide catalogue combined. "It is a peptide" carries no information about safety or efficacy in either direction. The are peptides safe page and peptides vs steroids take that further.

Key Takeaways

• The rule is three questions: built from amino acids, joined by peptide bonds into a chain, roughly fifty residues or fewer
• Tirzepatide is a peptide, 39 amino acids, with two Aib substitutions and a C20 fatty diacid tail. GLP-1 and glutathione are peptides too
• NAD and NAD+ are the same coenzyme in different redox states, and neither is a peptide. Enclomiphene is a SERM with no amino acid content at all
• Creatine is built from three amino acids but contains no peptide bond. Only glycine's skeleton survives; arginine donates a guanidino group and methionine a methyl group
• hCG fails only the length test: two chains of 92 and 145 residues, so a glycoprotein rather than a peptide
• Oral activity is the best quick heuristic. If it works as a plain tablet, it is probably not a peptide

Frequently Asked Questions

Is tirzepatide a peptide?

Yes. Tirzepatide is a synthetic 39 amino acid peptide built on the backbone of native GIP, with two substitutions of alpha-aminoisobutyric acid that stop DPP-4 clipping the N-terminus, and a C20 fatty diacid chain attached through a linker so the molecule binds albumin and lasts a week instead of minutes. Its molecular weight is roughly 4,800 daltons. At 39 residues it sits well inside the peptide range under any version of the peptide to protein convention, and it is a peptide in exactly the same sense that semaglutide, BPC-157 and oxytocin are.

Is NAD or NAD+ a peptide?

No, and not by a narrow margin. NAD+ is nicotinamide adenine dinucleotide, a coenzyme made of two nucleotides, nicotinamide mononucleotide and adenosine monophosphate, joined by a pyrophosphate bridge. It contains no amino acids and no peptide bonds, and at about 663 daltons it is a small molecule rather than a chain of anything. The plus sign records the oxidised state of the nicotinamide ring, not a charge on a peptide. NAD is grouped with peptides because it is sold by the same vendors, arrives as the same lyophilised powder and is reconstituted the same way, not because it shares any chemistry with them.

Is creatine a peptide?

No. Creatine is methylguanidinoacetic acid, a single small molecule of about 131 daltons with no peptide bond anywhere in it. The confusion comes from a true and widely repeated fact: the body builds creatine from three amino acids, glycine, arginine and methionine. But they are not strung together into a tripeptide. Glycine donates the carbon backbone, arginine donates only its guanidino group, and methionine donates only a methyl group by way of S-adenosylmethionine. Three amino acids contribute atoms; none ends up joined to another by an amide bond. Creatine peptide supplements are a separate thing again: creatine attached to short hydrolysed collagen peptides, a formulation choice rather than a statement about what creatine is.

Is glutathione a peptide?

Yes. Glutathione is a tripeptide, gamma-L-glutamyl-L-cysteinylglycine, at about 307 daltons. One of its two bonds is unusual: the glutamate joins the cysteine through its gamma-carboxyl side chain rather than its alpha-carboxyl, which makes that an isopeptide bond, while the cysteine to glycine link is an ordinary peptide bond. That side chain linkage is why ordinary aminopeptidases cannot cleave glutathione and why the body needs gamma-glutamyl transpeptidase to break it down. Glutathione is also assembled by two dedicated enzymes rather than by the ribosome, which does not stop it being a peptide.

What is the difference between a peptide and a protein?

Length, and the line is a convention rather than a chemical event. Both are chains of amino acids joined by peptide bonds. The common working rule is that roughly fifty residues or fewer is a peptide and anything longer is a protein, with some texts drawing the line at 100 residues or at a molecular weight around 5 to 10 kilodaltons instead. A softer structural criterion is often layered on top: proteins fold into a defined three dimensional shape their function depends on, while most peptides do not. Nothing happens to the chemistry at residue fifty-one. Insulin, at 51 amino acids across two chains, sits exactly on the line and gets called both.

Research use only. The compounds discussed are sold as research chemicals and are not approved for human use. Nothing here is medical advice.