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Sildenafil, sold under the brand name Viagra, is an inhibitor of phosphodiesterase type 5 enzyme (PDE5). It is an FDA-approved drug primarily indicated for the treatment of erectile dysfunction and pulmonary arterial hypertension. It is often prescribed off-label for female infertility and the Raynaud phenomenon. Furthermore, it has been shown to improve alopecia. Currently, it is being studied for its effect on urinary incontinence, skin reactions, and other conditions. At Pinnacle Peptides, sildenafil for sale is exclusively available for research and experimentation.

From Pubchem

IUPAC Name: 5-[2-ethoxy-5-(4-methylpiperazin-1-yl)sulfonylphenyl]-1-methyl-3-propyl-6H-pyrazolo[4,3-d]pyrimidin-7-one
Synonyms: 139755-83-2, Aphrodil, Vizarsin, Patrex
Molecular Formula: C22H30N6O4S
Molecular Weight: 474.6 g/mol
CAS number: 139755-83-2
PubChem CID: 135398744

Sildenafil was first developed by a group of scientists at Pfizer. They initially studied it for the management of angina and pulmonary arterial hypertension. Clinical trials on the drug didn’t show any significant effect on angina, but the researchers found that it can induce erection. Based on the discovery, Pfizer decided to market it for the treatment of erectile dysfunction. In 1998, it was approved by the FDA for erectile dysfunction following the successful completion of clinical trials.

Phosphodiesterase type 5 enzyme is responsible for catalyzing the breakdown of cGMP. Sildenafil mimics the action of cGMP and competitively binds to the active site of PDE5. This, in turn, prevents the PDE5 from metabolizing cGMP, resulting in the raised intracellular concentration of cGMP. The accumulation of cGMP in the cells increases the cGMP-dependent phosphatase kinase activity, leading to the phosphorylation of different proteins in the smooth muscles. It results in increased potassium efflux, and decreased intracellular calcium levels, thus causing relaxation of smooth muscles.

Relaxation of smooth muscle cells in the penis gland increases blood flow to the organ, thus causing erection. Similarly, vasodilation in pulmonary arterial hypertension leads to decreased resistance to blood flow. This, in turn, reduces the mean arterial pressure.

1. Raynaud Phenomenon

Raynaud Phenomenon is a medical condition characterized by the vasospasm in the toes and fingers in response to the cold or stress. It limits the blood flow to the affected areas, causing paleness, numbing and tingling. As sildenafil promotes the relaxation of smooth muscles in blood vessels, it might improve this condition. One study found that it effectively reduced the frequency of attacks in Raynaud phenomenon secondary to systemic sclerosis [1]. Furthermore, another study concludes that sildenafil is well-tolerated and effective for the treatment of RP [2].

2. Erectile Dysfunction

One study was designed to investigate the effect of sildenafil on sexual dysfunction associated with the use of antidepressants. Forty-nine female patients who were taking selective serotonin reuptake inhibitors were enrolled in the study. They were randomized to receive a placebo or sildenafil before engaging in sexual activity. The results found that the treatment significantly reduces the sexual side effects of antidepressants [3]. Similarly, another study found that sildenafil also improves erectile function and reduces sexual dysfunction associated with the use of SRIs in men [4].

Furthermore, research indicates that sildenafil shows promising results in the treatment of erectile dysfunction induced by spinal cord injury. However, the sacral or thoracolumbar region needs to be intact for successful results [5].

3. Alopecia

Sildenafil has demonstrated significant efficacy in the treatment of alopecia. One study revealed that it increased the vertical and terminal hair count in men with androgenic alopecia [6]. Furthermore, another study compared the effect of 5% minoxidil and 1% sildenafil on female pattern hair loss. Researchers observed that 1% sildenafil increased terminal and vellus hair count in the vertex, temporal, and frontal sides [7].

4. Exercise Capacity

Lack of oxygen delivery to muscles due to insufficient blood flow reduces exercise tolerance in patients with pulmonary hypertension. Since sildenafil induces vasodilation, it might improve exercise capacity in such patients. One study from SUPER trials found that sildenafil significantly improved peak VO2, peak O2 pulse, and PETCO2, indicating increased exercise tolerance [8].

5. Pulmonary Arterial Hypertension

Sildenafil has been already approved by the FDA for the treatment of WHO group 1 pulmonary arterial hypertension (PAH). Research shows that the combination of sildenafil and milrinone is effective for the PAH in neonates as compared to the sildenafil alone. Furthermore, it is recommended in resource-limited settings [9].

Patients with long-standing mitral valve disease often suffer from pulmonary arterial hypertension. Elevated arterial pressure in lungs during the mitral valve surgery has been shown to cause right ventricular failure. Sildenafil might ensure a safe and successful procedure. One study revealed that sildenafil administration before a surgical procedure can improve pulmonary arterial pressure before and after the surgery [10].

Sildenafil is a phosphodiesterase type 5 inhibitor used for the treatment of erectile dysfunction and PAH. It competitively binds to PDE5 and facilitates the relaxation of smooth muscles. It improves androgenic alopecia and exercise capacity in patients with PAH. At Pinnacle Peptides, we offer the option to purchase Viagra exclusively for research and educational institutions. This product is not intended for human consumption, only buy Viagra if you are a licensed researcher.

1. Herrick, A.L., et al., Modified-release sildenafil reduces Raynaud's phenomenon attack frequency in limited cutaneous systemic sclerosis. Arthritis & Rheumatism, 2011. 63(3): p. 775-782
2. Fries, R., K. Shariat, H.v. Wilmowsky, and M. Böhm, Sildenafil in the Treatment of Raynaud’s Phenomenon Resistant to Vasodilatory Therapy. Circulation, 2005. 112(19): p. 2980-2985.
3. Nurnberg, H.G., et al., Sildenafil Treatment of Women With Antidepressant-Associated Sexual Dysfunction: A Randomized Controlled Trial. JAMA, 2008. 300(4): p. 395-404.
4. Nurnberg, H.G., et al., Treatment of Antidepressant-Associated Sexual Dysfunction With Sildenafil: A Randomized Controlled Trial. JAMA, 2003. 289(1): p. 56-64.
5. Schmid, D.M., B. Schurch, and D. Hauri, Sildenafil in the Treatment of Sexual Dysfunction in Spinal Cord–Injured Male Patients. European Urology, 2000. 38(2): p. 184-193.
6. Al-Shabkhon, A.A., A.A. Halim Emam, and A. Abd Elfattah Afify, Comparative study between the efficacy of topical sildenafil and topical minoxidil in the treatment of male androgenic alopecia. QJM: An International Journal of Medicine, 2021. 114(Supplement_1).
7. Mostafa, H.A., H.A.K. Mohammed, and I. Fouda, Comparative Study Between the Efficacy and Safety of Topical Sildenafil Citrate Solution and Topical Minoxidil 5%in the Treatment of Female Pattern Hair Loss. 2022.
8. Oudiz, R.J., et al., Effect of sildenafil on ventilatory efficiency and exercise tolerance in pulmonary hypertension. European Journal of Heart Failure, 2007. 9(9): p. 917-921.
9. El-Ghandour, M., B. Hammad, M. Ghanem, and M.A.M. Antonios, Efficacy of Milrinone Plus Sildenafil in the Treatment of Neonates with Persistent Pulmonary Hypertension in Resource-Limited Settings: Results of a Randomized, Double-Blind Trial. Pediatric Drugs, 2020. 22(6): p. 685-693.
10. Villanueva, D.L.E., R.D. Agustin, and E.J. Llanes, Pre-Operative Sildenafil for Patients With Pulmonary Hypertension Undergoing Mitral Valve Surgery: A Systematic Review and Meta-Analysis. Cardiol Res, 2019. 10(6): p. 369-377.