Sildenafil (Viagra)

Structure: Pyrazolopyrimidinone PDE5 (phosphodiesterase-5) inhibitor. Blocks the enzyme that degrades cGMP, so nitric-oxide-driven smooth muscle relaxation persists longer in the corpus cavernosum and in vascular beds generally. Same mechanism as Tadalafil (Cialis), very different duration.

Dosage:

• Erectile function (as needed): 25-100mg, 30-60 minutes before activity. 50mg is the usual starting dose; 25mg if you are on other antihypertensives or a CYP3A4 inhibitor.
• Maximum: 100mg, once in 24 hours
• Pulmonary arterial hypertension (Revatio schedule): 20mg three times daily
• Low-dose daily (off-label, pumps and blood pressure): possible using the 20mg three-times-daily pattern, but most people chasing this effect switch to tadalafil because once-daily is far easier to adhere to

Administration:

• Oral tablet. A high-fat meal delays absorption by around an hour and drops peak concentration by roughly 30%, so take it fasted when onset speed matters.
• Onset 30-60 minutes, useful window around 4-6 hours
• Sexual stimulation is still required; it amplifies the response rather than creating one

Key Notes:

• Sildenafil versus tadalafil comes down to half-life. Sildenafil clears in a few hours and is an event drug. Tadalafil sits at 17.5 hours, reaches steady state on daily low doses, and gives the persistent pump and passive blood pressure reduction that bodybuilders use it for. Users who dislike a multi-day tail, or who get the tadalafil back ache, tend to prefer sildenafil.
• Nitrates are an absolute contraindication. Nitroglycerin, isosorbide, and recreational nitrites (poppers) combined with sildenafil can cause severe, treatment-resistant hypotension. This matters more than it sounds for enhanced athletes: chest pain on a heavy cycle is exactly the scenario where nitrates get administered.
• More PDE6 cross-reactivity than tadalafil. That is why blue or washed-out vision and light sensitivity occur with sildenafil specifically. Transient and dose-related, but a reason to stay at the lowest effective dose.
• CYP3A4 substrate. Ritonavir, ketoconazole, itraconazole, clarithromycin, and grapefruit raise levels substantially; halve the dose or avoid.
• Additive hypotension with alpha blockers (tamsulosin, doxazosin) and with other antihypertensives. Space doses and start low.
• Erectile dysfunction on cycle is usually hormonal, not vascular. Crashed oestradiol from over-dosed aromatase inhibitors, high prolactin from 19-nor compounds, and low free testosterone during a poorly planned PCT all cause it. A PDE5 inhibitor masks the symptom while the underlying picture stays broken. Pull the labs before reaching for a higher dose.
• Priapism (erection lasting over 4 hours) is a medical emergency; untreated it causes permanent tissue damage.
• Sudden vision or hearing loss is rare (non-arteritic anterior ischaemic optic neuropathy) but means stop and seek care immediately.
• Headache, flushing, nasal congestion, and dyspepsia are the common, benign side effects.

Bloodwork Monitoring:

• Sildenafil itself needs no routine bloodwork. It does not move hormones, lipids, liver enzymes, glucose, or haematology.
• If erectile dysfunction is why you are taking it, run the hormonal panel that explains it: Total Testosterone, Free Testosterone, Oestradiol, SHBG, and Prolactin.
• Add Haematocrit and Haemoglobin. Erythrocytosis raises blood viscosity and independently worsens erectile function; correcting it can resolve the problem without a PDE5 inhibitor.
• Blood pressure and resting heart rate logged at home are the real monitoring here, not a blood test.
• ALT and AST only if you are stacking hepatotoxic orals. Sildenafil is not hepatotoxic at normal doses.