Aspirin: Oral Bioavailability

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Felix Hoffman
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Why Aspirin Absorption Matters

When taking aspirin, you should aim to absorb as much of the drug as possible as quickly as possible, as this will lead to a higher concentration in your plasma in less time, which will relieve undesirable symptoms in the fastest and most effective manner.

Common Forms

Buffered aspirin absorbs faster with a higher availability than non-buffered aspirin, while enteric-coated aspirin has the slowest absorption.[1]  In solution, aspirin absorbs more rapidly with a higher bioavailability than otherwise.[2]  Even still, oral bioavailabilty of aspirin and water stands at just 68%.[3]  The aspirin solution’s acidity can damage your gut lining, so be sure to neutralize the aspirin first!

Alternative Solvents

Caffeine significantly increases absorption (25%) and plasma concentrations (17%) of aspirin.[4]

Taurine, a relaxing amino acid enhances aspirin absorption from the stomach and small intestine; homotaurine was needed for the absorption in the small intestine.[5]

Glycine, an amino acid similar to taurine enhances aspirin absorption by three-fold.[6]

Taken with aspirin, distilled alcohol and beer both increase its absorption and elimination rate, while tea increases just the elimination rate.  Milk and orange juice increases absorption with no effect on elimination.  Coffee affects neither absorption nor elimination.[7]

While orange juice does increase aspirin absorption, the former’s acidity will increase the chance of developing an ulcer, and alcohol will do the same.[8]   You should avoid orange juice or other acidic foods when taking aspirin.

For those wishing to avoid problems with oral consumption of aspirin, topical absorption exists as one such option.

Using acetone as a solvent, aspirin absorption goes to 21%, but the absorption rate decreases and the compound takes three to four days to completely absorb through human skin.

Water should also function as an effective solvent for aspirin, and thus aspirin may be added to one’s bathwater for absorption, or for greater efficiency, mixed with water into a 1% solution and applied as a lotion.

Diluted ethanol, such as with 40% grain alcohol may also be used as a solvent.  Antiseptic benefits to its use instead of water include protection of the solution from colonization from bacteria and fungus, such as mold, which inevitably occurs after a couple weeks of exposure to the air.

Distilled water, rather than tap water may prolong the life of the solution.

Caffeine (or coffee) may be mixed with the aspirin solution, as the two compounds synergize in their pro-thyroid action.  Coffee (or caffeine) and even low-doses of aspirin can dramatically lower blood sugar, so either should be consumed with plenty of carbohydrate, ideally sucrose, easily found in fruit, fruit juice, and table sugar.

One or two regular aspirin (325-650 mg) taken with a cup of coffee (50-100 mg caffeine) can attenuate the anxiogenic effects of the caffeine and will prevent negative side effects like jitters, anxiety, and racing thoughts, but always be wary of low blood sugar.

Note that while topical application of aspirin solution bypasses the gastrointestinal tract so that the aspirin crystals will not irritate the gut’s lining directly, it will still cause ulceration if the dose is not titrated appropriately due to aspirin’s inhibition of gastrointestinal mucosal COX activity.[1]

References (broken link)

[1] Lanas A, Scheiman J. Low-dose aspirin and upper gastrointestinal damage: epidemiology, prevention and treatment. Curr Med Res Opin. 2007 Jan;23(1):163–73.


  • Aspirin in water absorbs only 68%.
  • Amino acids taurine and glycine increase aspirin’s absorption rate.
  • Milk and orange juice increase aspirin absorption without speeding elimination.
  • Acidic foods (like oranges), liquids (like orange juice), and alcohol should not be consumed with aspirin.
  • Aspirin should be dissolved and neutralized.


[1] Latini R, Cerletti C, de Gaetano G, Dejana E, Galletti F, Urso R, et al. Comparative bioavailability of aspirin from buffered, enteric-coated and plain preparations. Int J Clin Pharmacol Ther Toxicol. 1986 Jun;24(6):313–8.

[2] Sagar KA, Smyth MR. A comparative bioavailability study of different aspirin formulations using on-line multidimensional chromatography. J Pharm Biomed Anal. 1999 Nov;21(2):383–92.

[3] Rowland M, Riegelman S, Harris PA, Sholkoff SD. Absorption Kinetics of Aspirin in Man follow Oral Administration of an Aqueous Solution. Journal of Pharmaceutical Sciences. 1972 Mar 1;61(3):379–85.

[4] Yoovathaworn KC, Sriwatanakul K, Thithapandha A. Influence of caffeine on aspirin pharmacokinetics. Eur J Drug Metab Pharmacokinet. 1986 Mar;11(1):71–6.

[5] Kimura T, Kim KS, Sezaki H. Effect of taurine on drug absorption from the rat gastrointestinal tract. J Pharmacobio-dyn. 1981 Jan;4(1):35–41.

[6] Murtaza G, Karim S, Najam-ul-Haq M, Ahmad M, Ismail T, Khan SA, et al. Interaction analysis of aspirin with selective amino acids. Acta Pol Pharm. 2014 Feb;71(1):139–43.

[7] Odou P, Barthélémy C, Robert H. Influence of seven beverages on salicylate disposition in humans. J Clin Pharm Ther. 2001 Jun;26(3):187–93.

[8] Kaufman DW, Kelly JP, Wiholm BE, Laszlo A, Sheehan JE, Koff RS, et al. The risk of acute major upper gastrointestinal bleeding among users of aspirin and ibuprofen at various levels of alcohol consumption. Am J Gastroenterol. 1999 Nov;94(11):3189–96.

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