Although Sildenafil (Viagra), vardenafil (Levitra), and Tadalafil powder (Cialis) all work by inhibiting PDE5, Tadalafil's pharmacologic distinction is its longer half-life (17.50 hours) – compared to Sildenafil (4.0–5.0 hours) and vardenafil (4.0–5.0 hours) – resulting in longer duration of action, and so partly responsible for "The Weekend Pill" sobriquet. Furthermore, the longer half-life is the basis for current investigation of tadalafil's daily therapeutic use in relieving pulmonary arterial hypertension. Sildenafil is approved in several world regions as a thrice-daily therapy for pulmonary arterial hypertension.

A high-pressure liquid chromatography-diode array detection and multi-mode ionization tandem mass spectrometry (HPLC-DAD-MMI-MS/MS) method was used to identify tadalafil and rimonabant in electronic cigarette (e-cigarette) cartridges. Amino-tadalafil is a drug similar of the commercially approved ™ (i.e. tadalafil). Rimonabant is a drug that was, at one time, approved for weight loss in Europe (although approval has been retracted), but not in the United States. In addition, poor quality control over the e-cigarette products analyzed here is shown by the presence of nicotine in products labeled as containing no nicotine or by the presence of significant amounts of rimonabant oxidative degradant in e-cigarette products containing rimonabant. Identification was accomplished by comparing the retention time of relevant peaks in the sample with those of standard compounds, in addition to comparison of the UV spectra, mass spectra and/or product ion mass spectra.