Sildenafil

The blue pill was marketed by Pfizer as DE-agent and recently studies as preventive of premature ejaculation Graciano et al (2017) present a mechanism for hepatotoxicity of this medicine, also many counterfeit plant preparations, involving CYP3A4 enzymes Further questions remains Phosphodiesterase-5 (PDE-5) inhibitors, such as sildenafil, were approved for treatment of pulmonary arterial hypertension (PAH) by the Food and Drug Administration (FDA) in 2005, which holds promise in improving quality of life and therefore making this class of medications effective palliative therapy agents

Links
comparable efficacy shows tadalafil a recent study excluded tadalafil
 * Preeclampsia

PH
Treatment with oral sildenafil 40 mg t.i.d. for 6 months in patients with persistent PH after successful correction of VHD is associated to unfavourable clinical outcomes as compared to placebo

Bosentan
McLaughlin V, Channick RN, Ghofrani HA, Lemarié JC, Naeije R, Packer M, Souza R, Tapson VF, Tolson J, Al Hiti H, Meyer G, Hoeper MM. Bosentan added to sildenafil therapy in patients with pulmonary arterial hypertension. Eur Respir J. 2015 Aug;46(2):405-13. doi: 10.1183/13993003.02044-2014. Epub 2015 Jun 25. PMID: 26113687.

Immune system
..can affect innate and adaptative immune systems