Sublingual and ODT Tirzepatide and Semaglutide: Why Peptides Are Hard to Absorb, What Rybelsus Needed to Work, and What the Compounded Tablets Have Not Shown

The problem with peptides and mouths

Semaglutide is a 31-amino-acid peptide with a fatty-acid side chain; tirzepatide is 39 amino acids with a similar chain. Peptides of this size face two barriers when taken by mouth. Digestive enzymes in saliva, the stomach and the gut cut them apart, and even intact, molecules of about 4,000 daltons with charged side groups cross the lipid membranes of mucosal cells very poorly. Insulin, a 51-amino-acid peptide, has resisted oral formulation for a century for the same reasons. That is why the approved GLP-1 medications are injected: subcutaneous bioavailability for tirzepatide is about 80%, and the drug reaches the blood intact.

The sublingual route — under the tongue — avoids stomach acid and first-pass liver metabolism, which is why it works for small, lipophilic molecules such as nitroglycerin. It does not avoid the membrane problem. The oral mucosa is a barrier to large hydrophilic peptides, and a tablet or troche that dissolves under the tongue delivers a peptide to a surface it cannot cross in meaningful amounts, before it is swallowed and digested.

What it took to make oral semaglutide work

Novo Nordisk spent more than a decade on oral semaglutide, and the result shows what the problem demands. Rybelsus co-formulates semaglutide with SNAC (salcaprozate sodium), an absorption enhancer that raises the local pH in the stomach to protect the peptide from pepsin and transiently increases the permeability of gastric mucosa so that semaglutide is absorbed across the stomach lining — not the intestine, and not the mouth. The tablet must be taken on an empty stomach with no more than 4 ounces of water and nothing else for 30 minutes, because food or extra water dilutes the SNAC effect. Even so, absolute bioavailability is about 1%, and it is variable. To compensate, the doses are enormous relative to injection: Rybelsus is 3 to 14 mg daily, oral Wegovy is 25 mg daily, and OASIS 1 tested 50 mg daily — against 0.25 to 2.4 mg weekly by injection.

Oral Wegovy at 25 mg produced about 13.6% weight loss in its trial program, close to the injectable's 14.9%, and was approved in December 2025. That is the benchmark for what an oral GLP-1 with real absorption data looks like: a proprietary enhancer, a dose 10 to 100 times the injected dose, an administration ritual, measured blood levels, and a trial.

What the compounded sublingual products have shown

Nothing that has been published. We searched for pharmacokinetic data — measured plasma semaglutide or tirzepatide concentrations after sublingual or ODT administration of a compounded product — and found none in the peer-reviewed literature. We found no randomized trial, no controlled cohort, and no FDA submission. What exists is marketing (convenience, no needles, "same medication") and anecdote.

The absence is telling because the study is easy. A pharmacokinetic comparison — a dozen volunteers, a sublingual dose, a series of blood draws — is the kind of study a compounding pharmacy or a telehealth provider selling the product could commission for a modest sum. That none has been published, in a market worth billions, is consistent with the products not achieving the levels that would make a publishable result.

The possible outcomes for a patient

If a sublingual product delivers little or no drug, the patient experiences no effect and no side effects, and pays for the product. If it delivers a small, variable amount, the patient may experience a weak, inconsistent effect. If it somehow delivered a substantial amount — which the chemistry argues against — the patient would have the effect of an injected dose with none of the dosing precision. None of these is a good outcome relative to a $139 injection, and the products cost more: NexLife's ODT tirzepatide is $199 to $229 per month against $139 to $169 for the injection, and its ODT semaglutide $165 to $199 against $119 to $139. Other providers price sublingual forms similarly. The premium buys a route of administration without evidence that the route works.

How we treat sublingual products in the database

We list every sublingual and orally disintegrating product we know of in the pricing database with its price and verification status, because a complete candidate universe is the point of the database, and we exclude all of them from rankings, because there is no pharmacokinetic evidence that they deliver a predictable dose. That policy applies to NexLife's ODT plans, whose prices we have verified, in exactly the way it applies to every other provider's; a verified price for an unproven product is still an unproven product. A reader who chooses one should understand what they are buying: a product whose absorption may be a small fraction of the labelled amount, at a price that at most providers exceeds the injectable, and with no trial data to set expectations for weight loss. If a provider publishes measured blood levels from its sublingual product at a stated dose, with the method and the number of patients, we will record the study on the sources page and revisit the policy. Until then the injectable products at approved doses are the only ones with evidence, and the semaglutide and tirzepatide references describe what that evidence shows.

Why they are sold

Convenience and needle aversion are real; a meaningful fraction of patients will not inject. And, as with microdosing, the post-shortage rules create a regulatory reason: a dosage form the approved products do not come in is a formulation that "differs," which is what a pharmacy must show to compound after the FDA ended the shortages. The dosage form serves the compounding rationale whether or not it serves the patient.

What to ask a provider

If a provider offers a sublingual or ODT GLP-1: Do you have pharmacokinetic data for this product? What plasma levels does it achieve, and how do they compare with injection? Has the formulation been tested in any trial? A provider with a plausible product would have blood-level data to show. A provider without it is selling a hypothesis. For a patient who will not inject, the FDA-approved oral Wegovy tablet has measured bioavailability and a trial, and our oral Wegovy guide compares its cost with compounded options. Eli Lilly's orforglipron, a non-peptide oral GLP-1 agonist in late-stage development, is the route by which a tirzepatide-class oral drug will eventually arrive; sublingual compounded tirzepatide is not.

We rank standard injectable plans for these reasons and list sublingual plans in the pricing database with their status.

Sources

1. Rybelsus (semaglutide tablets) prescribing information, clinical pharmacology section (absolute bioavailability approximately 1%)
2. Buckley ST et al. Transcellular stomach absorption of a derivatized glucagon-like peptide-1 receptor agonist. Sci Transl Med 2018;10:eaar7047
3. Knop FK et al. Oral semaglutide 50 mg taken once per day in adults with overweight or obesity (OASIS 1). Lancet 2023;402:705-719
4. Wegovy tablets (oral semaglutide 25 mg) prescribing information, December 2025
5. Zepbound prescribing information, clinical pharmacology (subcutaneous bioavailability approximately 80%)
6. U.S. FDA, FDA's concerns with unapproved GLP-1 drugs used for weight loss

Citations are to primary sources (peer-reviewed trials, FDA labeling and announcements, and provider pricing pages). See our sources policy and corrections log.