Research

Oral, nasal and topical peptides: what the route changes

Almost every approved peptide drug is injected, and the exceptions show why. The one semaglutide tablet on the market needed a built-in absorption enhancer to get roughly one percent of the dose into the blood, and it comes with instructions that are part of the product.

By Nora Castellan, Standards EditorUpdated September 2026

The needle is a chemistry result, not a marketing choice

A peptide is a short chain of amino acids, which is also a description of food. The digestive tract exists to take chains like that apart, and it is very good at it.

That is the whole reason injection is the default. Swallowing a peptide puts it into the one environment specifically built to dismantle it, and what survives still has to cross the gut wall, which is selective about size.

So when a capsule, a spray or a cream turns up carrying the same compound name as an injection, the first question is not whether it is cheaper or easier. It is whether anything arrives.

What it took to make one peptide work as a tablet

Oral semaglutide is the clearest case study available, because it exists, it is approved, and its label publishes the numbers.

The tablets are co-formulated with SNAC, salcaprozate sodium, which the label describes as facilitating absorption after oral administration. Absorption predominantly occurs in the stomach rather than further down. That is a purpose-built delivery system, not semaglutide put into a capsule.

With that system in place, the label states an estimated absolute bioavailability of approximately 0.4 to 1 percent for the Rybelsus tablets and 1 to 2 percent for the Ozempic tablets.

Read that plainly. A dedicated absorption enhancer, a formulation designed around where in the gut it dissolves, and a full approval program deliver roughly one percent. The other ninety-nine percent never reaches the bloodstream.

The instructions are part of the formulation

Because so little gets through, the conditions of taking it stop being advice and become part of the product. The label prints them as administration requirements.

The tablet is taken on an empty stomach in the morning with water, up to four ounces, and with no other liquid. It is swallowed whole, not split, crushed, chewed or dissolved in anything. Then at least thirty minutes pass before any food, any beverage, or any other oral medication.

The label also says the two tablet products are not substitutable on a milligram-for-milligram basis with each other. Same molecule, same route, same manufacturer, and still not a straight swap.

Any oral or sublingual peptide product that arrives without instructions of this specificity is telling you something. Either the absorption problem was solved and the solution has conditions, or it was not addressed.

The nose is a real route, and a lossy one

Nasal delivery genuinely works for some peptides, and two approved products show what it costs and what it depends on.

Calcitonin salmon is a peptide hormone available as both an injection and a nasal solution. The nasal label puts its mean bioavailability at approximately 3 percent of the injectable in healthy subjects. Its pharmacokinetics section gives 3 to 5 percent relative to intramuscular administration. Absorption through the nasal mucosa peaks at about 13 minutes.

Desmopressin, another peptide, is approved as a nasal spray for central diabetes insipidus, and its label is unusually direct about the route's dependency. It is not indicated for patients whose conditions compromise the intranasal route. It warns that nasal mucosa abnormalities may cause erratic, unreliable absorption. The label names scarring and edema from chronic use, nasal blockage, mucosal atrophy, severe atrophic rhinitis and recent nasal surgery.

That is the trade in one sentence. A mucosal route can deliver a peptide without a needle, at a fraction of the injected exposure, and only while the mucosa is in the condition the studies assumed.

A format is not a formulation

Capsules, sublingual drops, nasal sprays and creams carrying peptide names appear throughout this market, often at prices that undercut the injectable version of the same compound.

The figure that would settle whether such a product delivers anything is absolute bioavailability, and it lives in section 12.3 of an approved product label. That section exists because an approval program required the measurement. For the compounds this site covers that have no approved product anywhere — and each compound's status page states which those are — there is no 12.3 to read.

What is left is a format claim. A capsule looks like a supplement, a spray looks like a decongestant, and a cream looks like skincare. None of those appearances says anything about whether the molecule crossed a membrane.

The two approved non-injected peptide products above are the reference class. Both needed a specific engineered formulation, both publish a single-digit or low-single-digit percentage, and both attach conditions to getting even that.

Topical is a different regulatory question as well as a different route

Skin adds a second layer to the problem, because a product applied to skin may not be a drug at all in regulatory terms.

GHK-Cu is the compound where this shows up most sharply on this site. A copper-peptide serum sold off a shelf and an injectable vial ordered through a telehealth program are two different purchases. They are priced on different units and sold through different channels, and the comparison page for that pair sets them side by side.

The regulatory record itself is route-aware. In FDA's Category 2 table, the GHK-Cu entry is scoped specifically to injectable routes of administration. The agency is not treating "GHK-Cu" as one thing; it is treating a route as part of the substance's identity for compounding purposes.

That is worth carrying into any product page. A study, a status, a price and a safety statement can each be true of one route and silent about another.

What the route does to a price comparison

This site compares sellers on price per milligram wherever the unit can be established, because it is the only figure that lets two listings of the same compound be set against each other.

A change of route breaks that comparison quietly. If one product is injected and another is swallowed, the milligrams on the two labels are not the same kind of quantity. One is an amount administered where nearly all of it reaches circulation. The other is an amount where a small percentage does.

The approved oral and nasal labels are the proof that the gap is large rather than a rounding detail. Roughly one percent for the tablets, roughly 3 to 5 percent for the nasal solution against intramuscular.

So a cheaper capsule is not a cheaper version of an injection. It is a different product whose comparable unit has not been established, and treating the two as tiers of one purchase is the error the price stopped you from noticing.

What to check on any non-injected peptide offer

Ask whether an approved product exists for that compound by that route. That is the only place a measured absorption figure comes from.

If a percentage is quoted, ask what it is a percentage of. A share of an injected dose and a share of the amount swallowed are different claims, and only one of them is bioavailability.

Look for the conditions. A real oral or mucosal formulation carries administration requirements, because the delivery only works inside them.

Check that the route in the cited research matches the route in the cart. A result obtained by injection in a study says nothing about a cream, and this is the most common mismatch in the category.

Do not convert a price across routes. Per-milligram comparisons hold within a route and fall apart across one.

Your own instructions come from your prescriber and the leaflet in your carton. Nothing here is a schedule or a method to follow.

Key takeaways

Injection is the default route because the digestive tract is built to break peptide chains apart.
Oral semaglutide needed a co-formulated absorption enhancer to reach roughly 0.4 to 2 percent absolute bioavailability.
Its administration conditions — fasting, water only, whole tablet, a thirty-minute wait — are part of the formulation.
Calcitonin salmon nasal solution runs about 3 percent of the injectable, and 3 to 5 percent relative to intramuscular.
The desmopressin nasal label warns that damaged nasal mucosa makes absorption erratic and unreliable.
FDA's Category 2 entry for GHK-Cu is scoped to injectable routes, so route is part of the regulatory question.
Price per milligram compares listings within a route and stops meaning anything across one.

Frequently asked questions

Do oral peptides work?

One approved example shows what it takes. Oral semaglutide tablets are co-formulated with SNAC, an absorption enhancer, and are absorbed predominantly in the stomach. Their estimated absolute bioavailability is about 0.4 to 1 percent for one tablet product and 1 to 2 percent for the other. That is with a dedicated delivery system and a full approval program behind it. An oral version of a compound with no approved product has no equivalent measurement to point at.

Why do the oral semaglutide instructions matter so much?

Because the formulation only works inside them. The label directs the tablet to be taken on an empty stomach in the morning, with water only and up to four ounces. It is swallowed whole rather than split, crushed, chewed or dissolved. At least thirty minutes then pass before any food, drink or other oral medicine. When roughly one percent of a dose is getting through, the conditions around it are load-bearing rather than optional.

Is a nasal spray a good way to take a peptide?

It can be, for a peptide with an approved nasal product. Calcitonin salmon nasal solution has a mean bioavailability of about 3 percent of the injectable, and 3 to 5 percent relative to intramuscular administration. The desmopressin nasal spray label adds the other half of the picture. Nasal blockage, mucosal atrophy, scarring, severe atrophic rhinitis or recent nasal surgery may make absorption erratic and unreliable. The product is not indicated where the route is compromised.

Is a peptide cream the same product as the injectable version?

No, and the regulatory record treats them separately. A copper-peptide serum bought off a shelf and an injectable vial ordered through a telehealth program are different purchases sold through different channels on different pricing units. FDA's Category 2 entry for GHK-Cu is itself scoped to injectable routes of administration, which is a regulator writing the route into the substance's identity rather than treating the compound as one undifferentiated thing.

Can I compare the price of a capsule with the price of a vial?

Not on a per-milligram basis. Price per milligram only compares listings that deliver the drug the same way. When roughly one percent of an oral dose and nearly all of an injected dose reach circulation, the milligram on each label is a different quantity, so the cheaper number is not the cheaper product. Compare within a route and treat a change of route as a change of product.

Why is sublingual delivery offered for peptides that have no oral product?

Because the format is easy to produce and the claim is easy to make. Under-the-tongue delivery is a real pharmaceutical route, but a route becomes a product only through a formulation designed for it. The measurement that shows it worked appears in the clinical pharmacology section of an approved label. Where no approved product exists for that compound by that route, that section does not exist for it either, and a sublingual claim rests on something other than a reviewed absorption study.

Sources

Each document below is named as it names itself, with the date printed on that document rather than the day it was read.

RYBELSUS and OZEMPIC (semaglutide) tablets — FDA-approved prescribing information — National Library of Medicine, DailyMed, January 2026
Calcitonin salmon nasal solution — FDA-approved prescribing information — National Library of Medicine, DailyMed, June 2026
Desmopressin acetate nasal spray — FDA-approved prescribing information — National Library of Medicine, DailyMed, August 2025
OZEMPIC (semaglutide) injection — FDA-approved prescribing information — National Library of Medicine, DailyMed, June 2026
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — U.S. Food and Drug Administration, April 2026