Ibuprofen is a propionic acid derivative, a non-steroidal anti-inflammatory drug with a very effective anti-inflammatory and analgesic action and an significant antipyretic effect. It is a non-selective strong inhibitor of both Cyclooxygenase isoforms, Cyclo-oxygenase-1 (COX-1) and Cyclooxygenase-2 (COX-2). The main purpose of this research was to establish the accuracy of the official Ibuprofen amount calculated on the pharmaceutical tablet, according to the Rules of Good Pharmaceutical Practice provided by the European and Romanian Pharmacopoeias. Ibuprofen real concentrations can also be exactly found from various unknown pharmaceutical samples, according to the Official Pharmacopoeias Rules. Color reaction occurred quantitatively between Ibuprofen with alpha-naphthylamine ethanolic solution 0.1% , sodium nitrite NaNO₂ aqueous solution 4-5% , by heating at a high temperature of 70-75ºC , which led to the quantitative synthesis of an intense orange-yellowish azo dye that was spectrophotometrically analyzed at its maximum assigned absorption wavelength, λ = 460 nm. The pure Ibuprofen amount on the pharmaceutical tablet was calculated at λ.=460 nm for both pharmaceuticals and was found to be 611,750 mg, assigned to a mean percentage content of 101,958% active substance for the first pharmaceutical product, very close to the officially declared amount (600 mg), with a average percentage error of only 1,958 % in addition to the stated active substance content. For the second pharmaceutical product, pure Ibuprofen content was calculated and assigned to 394,774 mg for a mean percentage content of 98,694% , close enough to the official declared amount (400 mg). The average percentage error was only 1,307 % less than the officially declared active substance content. The Ibuprofen amounts found in both pharmaceuticals were within the normal range of values, located below ± 5%, which is the official maximum percentage deviation mentioned in European and Romanian Pharmacopoeias. Ultimately, both spectrophotometric methods were statistically validated.