First-Pass Effect in Supplements: Why Dosage Form Matters

July 30, 2026

By Jack Zheng, MS Pharmacy -- Founder of MIHIYO Labs

Summary

The first-pass effect in supplements is the share of a dose that gets metabolized in the gut wall and liver before it reaches systemic blood. For some actives it barely matters; for others it changes the whole dosage-form decision. In healthy volunteers, oral melatonin showed only about 15% absolute bioavailability, and a 2023 crossover study found a sublingual melatonin spray reached peak levels sooner and at higher exposure than a prolonged-release oral tablet. That is why an oral dissolving strip (ODS) can matter. For MIHIYO Labs, dosage form is not packaging. It is part of the pharmacology.

What is the first-pass effect in supplements?

The first-pass effect in supplements means part of a swallowed dose is metabolized before it reaches the bloodstream that circulates through the rest of the body. The key point is practical, not academic. If the active survives the gut and liver easily, changing dosage form may mostly change timing. If the active is heavily metabolized on that first trip, the route can change both onset and total exposure.¹²

Bioavailability is the fraction of a dose that reaches systemic circulation unchanged. For a swallowed product, that final number reflects several steps in series: how much of the dose gets absorbed, how much escapes metabolism in the intestinal wall, and how much survives the liver before entering systemic blood.¹² That is why first-pass is more than a generic "the liver breaks some of it down" slogan. It is a route problem with multiple checkpoints.

For a supplement buyer, the simple translation is this: dosage form matters most when the active is low-dose, timing-sensitive, or easy to metabolize before it reaches the rest of the body. That is one reason I do not treat dosage form as decorative packaging. If the bottleneck is pharmacokinetic, adding milligrams is often a cruder fix than changing the route.

Where does the dose get lost: gut wall or liver?

A swallowed tablet, capsule, gummy, or liquid does not go straight from the mouth to the bloodstream. It first has to disintegrate or dissolve, then cross the intestinal lining, then move through the portal vein to the liver. Only after that first hepatic pass does the surviving fraction enter systemic circulation.¹² When people say a product is "oral," they usually compress all of those steps into one word, but those steps are exactly where route-level differences come from.

The liver is the best-known first-pass site, but it is not the only one. Pond and Tozer laid out the clinical logic decades ago: first-pass elimination can occur at multiple sites between administration and blood sampling, including the gastrointestinal tract itself.¹ Kwan later framed oral bioavailability as the integrated result of absorption plus losses in the gut lumen, gut wall, and liver.² For supplement buyers, that means poor oral performance does not automatically mean "bad ingredient." Sometimes the molecule is fine and the route is doing the damage.

An oral dissolving strip works differently. If part of the dose is absorbed across the oral mucosa, that fraction can enter systemic veins before the dose reaches the portal circulation. It is not a perfect bypass. Some of the dose is still swallowed, saliva still matters, and not every ingredient permeates the oral mucosa well enough to justify a strip. But the route gives a formulator a chance to reduce gut-wall and hepatic loss for the absorbed fraction instead of forcing the whole dose through the usual swallow-first pathway.⁵⁶

Two human examples make the mechanism tangible. Oral melatonin tablets showed only about 15% absolute bioavailability in healthy volunteers, which is exactly the kind of result that tells you first-pass may be a real design constraint.³ Nitroglycerin is the more extreme classic example: oral doses in one human study were less than 1% bioavailable, which is why the drug became a textbook case for alternative routes rather than a model for swallowed delivery.⁷ Those are different molecules and different use cases, but they teach the same lesson. Route can dominate outcome.

What do the pharmacokinetic studies actually show?

The cleanest way to understand first-pass effect supplements is to compare route-level outcomes instead of repeating the definition.

Route or format	First-pass burden	Representative human PK result	What a buyer should infer	Source
Swallowed melatonin tablet	Full gut-wall and hepatic first pass	Oral melatonin showed about 15% absolute bioavailability in healthy volunteers	A low-dose active can lose a lot of exposure before systemic circulation	DeMuro et al., 2000³
Sublingual melatonin spray vs oral prolonged-release tablet	Lower first-pass exposure for the absorbed mucosal fraction	Sublingual spray Cmax 2332 pg/mL and Tmax 23.3 min vs oral tablet Cmax 1151 pg/mL and Tmax 64.2 min	Route can change both speed and exposure even at a lower dose	Ait Abdellah et al., 2023⁴
Buccal or sublingual buprenorphine	Oral route is limited enough that mucosal delivery is favored	Buccal film showed 46% to 51% absolute bioavailability; sublingual exposure was about 30% in a separate human study	A transmucosal route can recover useful exposure when ordinary oral bioavailability is poor	Bai et al., 2016; Mendelson et al., 1997⁵⁶
Oral nitroglycerin	Overwhelming first-pass loss	Oral nitroglycerin was less than 1% bioavailable in capsule and solution forms	Some molecules are bad candidates for swallowed delivery on principle	Noonan and Benet, 1986⁷
Sublingual film examples with first-pass-sensitive actives	Designed to bypass part of hepatic loss	Salbutamol film Tmax 0.75 h vs tablet 2.1 h; terbutaline film relative bioavailability 204.08% vs oral tablet	Film formats help most when the molecule and dose are suitable for mucosal delivery	Sallam et al., 2017; Sayed et al., 2013⁸⁹

Melatonin is the most useful supplement-adjacent example because the active is familiar and the dose is small. DeMuro and colleagues found that oral melatonin had only about 15% absolute bioavailability in healthy volunteers.³ That number does not prove the whole problem is hepatic first-pass, because poor absorption can contribute too. But it does show why route deserves attention. In the 2023 crossover study by Ait Abdellah and colleagues, an immediate-release sublingual spray reached a much earlier peak and a higher peak concentration than a prolonged-release oral tablet, while the plasma melatonin to 6-sulfatoxymelatonin ratio also favored the sublingual form.⁴ That is exactly the pattern you would expect when more of the active reaches systemic blood before heavy hepatic transformation.

The buprenorphine papers matter for a different reason. They show the principle very clearly. Bai and colleagues reported 46% to 51% absolute bioavailability from a buccal film in healthy volunteers, while Mendelson and colleagues found about 30% bioavailability after sublingual exposure in a separate human study.⁵⁶ Those are not supplement trials, and I do not present them as if they were. I use them because they make the route logic visible: when the swallowed route is inefficient, the oral mucosa can recover clinically meaningful exposure.

The nitroglycerin paper is the warning label for anyone who thinks first-pass is a trivial detail. Less than 1% oral bioavailability is a route failure, not a small optimization issue.⁷ Most supplements are not that extreme, but the paper is still useful because it shows the outer limit of what first-pass can do. Once you have seen a molecule fail that badly by mouth, it becomes easier to understand why a low-dose hormone-like supplement or other route-sensitive active might deserve a more careful dosage-form decision.

The salbutamol and terbutaline film studies bring the argument back toward dosage forms a supplement buyer can recognize. Sallam and colleagues found a salbutamol sublingual film reached peak concentration at 0.75 hour versus 2.1 hours for the tablet comparator.⁸ Sayed and colleagues reported a terbutaline sublingual film with 204.08% relative bioavailability versus conventional oral tablets.⁹ Those papers do not mean every strip is automatically superior. They mean a strip becomes interesting when oral first-pass is part of the bottleneck and the dose is suitable for mucosal delivery.

What this means for MIHIYO products

For MIHIYO products, the first-pass question is most relevant when the active is low dose and the route itself is part of the value proposition. That is why Sleep-Support is a better example than a high-dose mineral would be. A low-dose melatonin format can benefit from reducing swallowed loss and from producing a more useful early exposure curve, which is also why the earlier MIHIYO article on melatonin strip dosage keeps coming back to bioavailability rather than milligram theater.

The same principle does not apply equally to every ingredient. If an active already performs well as an ordinary swallowed dose, the strip format may still help with timing, portability, or water-free use, but it is less honest to sell it as a first-pass rescue story. That is a concrete formulation boundary I care about. I would rather use the strip where route sensitivity is real than force every ingredient into the same narrative.

This is also why I think the best internal comparison is still oral dissolving strip vs capsule, not strip versus some imaginary average supplement. The route only matters in context. The dosage-form question is: what is the active, what dose is required, how much of the effect depends on early exposure, and what part of the route is actually limiting the result? If that answer points to first-pass, a strip earns its keep. If it does not, the strip needs a different reason to exist.

Where this concept gets oversimplified

The first oversimplification is saying that a strip "bypasses first-pass" as if the whole dose instantly teleports past the liver. That is not how it works. Some of the dose is usually swallowed, oral contact time is finite, and mucosal permeability is molecule-specific.⁵⁶⁸⁹ The real claim is narrower: the absorbed mucosal fraction can reduce gut-wall and hepatic loss compared with a fully swallowed route.

The second oversimplification is treating first-pass as the only reason dosage forms differ. Disintegration time, dissolution, food effects, local pH, transporter biology, saliva, and dose load all matter too.¹² A dosage form can fail because it releases the active too slowly, because the molecule is unstable, because the dose is too large for the route, or because user behavior is inconsistent. First-pass is an important mechanism. It is not a universal answer.

The third oversimplification is translating drug-route data straight into supplement certainty. The best human pharmacokinetic illustrations in this article include melatonin, buprenorphine, nitroglycerin, terbutaline, and salbutamol.³⁴⁵⁶⁷⁸⁹ That is a mixed evidence set on purpose. It gives a defensible mechanism article, but it is not a direct clinical trial on finished MIHIYO retail products. I think it is better to say that plainly than to borrow a drug paper and pretend it proves a supplement claim the study never tested.

The bottom line

The first-pass effect supplements question is really a dosage-form question. A swallowed product has to survive absorption, gut-wall metabolism, and hepatic metabolism before the rest of the body sees the dose.¹² A strip, buccal film, or sublingual route can change that equation for the fraction absorbed through the oral mucosa.⁴⁵⁶ My formulation view is simple: use that advantage where the molecule truly needs it, not where it only sounds sophisticated. Dosage form matters most when route is the bottleneck, and that is exactly when first-pass stops being theory and starts being product design.

References

Pond SM, Tozer TN. First-pass elimination. Basic concepts and clinical consequences. Clin Pharmacokinet. 1984;9(1):1-25. PMID: 6362950 / DOI: 10.2165/00003088-198409010-00001. <https://pubmed.ncbi.nlm.nih.gov/6362950/>
Kwan KC. Oral bioavailability and first-pass effects. Drug Metab Dispos. 1997;25(12):1329-1336. PMID: 9394021. <https://pubmed.ncbi.nlm.nih.gov/9394021/>
DeMuro RL, Nafziger AN, Blask DE, Menhinick AM, Bertino JS Jr. The absolute bioavailability of oral melatonin. J Clin Pharmacol. 2000;40(7):781-784. PMID: 10883420 / DOI: 10.1177/00912700022009422. <https://pubmed.ncbi.nlm.nih.gov/10883420/>
Ait Abdellah S, Raverot V, Gal C, Guinobert I, Bardot V, Blondeau C, Claustrat B. Bioavailability of Melatonin after Administration of an Oral Prolonged-Release Tablet and an Immediate-Release Sublingual Spray in Healthy Male Volunteers. Drugs R D. 2023;23(3):219-229. PMID: 37438493 / DOI: 10.1007/s40268-023-00431-9. <https://pubmed.ncbi.nlm.nih.gov/37438493/>
Bai SA, Xiang Q, Finn A. Evaluation of the Pharmacokinetics of Single- and Multiple-dose Buprenorphine Buccal Film in Healthy Volunteers. Clin Ther. 2016;38(2):358-369. PMID: 26804639 / DOI: 10.1016/j.clinthera.2015.12.016. <https://pubmed.ncbi.nlm.nih.gov/26804639/>
Mendelson J, Upton RA, Everhart ET, Jacob P 3rd, Jones RT. Bioavailability of sublingual buprenorphine. J Clin Pharmacol. 1997;37(1):31-37. PMID: 9048270 / DOI: 10.1177/009127009703700106. <https://pubmed.ncbi.nlm.nih.gov/9048270/>
Noonan PK, Benet LZ. The bioavailability of oral nitroglycerin. J Pharm Sci. 1986;75(3):241-243. PMID: 3084757 / DOI: 10.1002/jps.2600750306. <https://pubmed.ncbi.nlm.nih.gov/3084757/>
Sallam NM, Sanad RA, Kharshoom RM, Zeneldin MA. Development of Salbutamol Sulphate Sublingual Films in Pullulan Matrix for Enhanced Bioavailability & Clinical Efficacy. Curr Drug Deliv. 2017;14(3):390-397. PMID: 27784211 / DOI: 10.2174/1567201813666161024161308. <https://pubmed.ncbi.nlm.nih.gov/27784211/>
Sayed S, Ibrahim HK, Mohamed MI, El-Milligi MF. Fast-dissolving sublingual films of terbutaline sulfate: formulation and in vitro/in vivo evaluation. Mol Pharm. 2013;10(8):2942-2947. PMID: 23883311 / DOI: 10.1021/mp4000713. <https://pubmed.ncbi.nlm.nih.gov/23883311/>