If I was interested in tadalafil (I’m definitely not!), this is what would stop me dead in my tracks - the pretty high risk of eye problems, and even hints of ototoxic effects (hearing). Even if you don’t experience diagnosable severe pathology, it may still put detectable strain on your eyes (10% of users), and who knows what is happening that you’re not feeling in the moment - no thanks. YMMV.
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I have looked at the pleitropic effects related to brain vasculature this one provides, and according to AI, the risk of hypotension doesn’t make it worth it for me. My BP is about 99/65, and a combination of SGLT2 inhibitor + GLP-1 RA + Rosuvastatin + Ezetimibe is already providing microvascular, endothelial, and neuro-inflammatory protection.
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Actually, if you take this drug with a low BP, it might lower your BP inside your heart and might cause a massive heart attack. This one to be prescribed under a doctor’s supervision that knows what they’re doing IMO (checking medical history & other prescriptions).
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Key point. If your current stack already covers a given area, there is absolutely no reason to take onboard another agent that addresses the same area, unless you are doing a substitution because the new agent is clearly superior (stack re-adjustment). You are increasing risks with no advantage. In my business we call that “a hat on a hat” - if you are already wearing a hat there is no point in putting on another one, you can only make it worse. This is a kind of plague in the biohacker space - constant reports that some drug or other has “a benefit” and folks rush to take it without asking whether they need that “benefit”, even if the benefit is real. Establish your stack with the best evidence and fitted to your requirements, and if another drug comes along, ask why you should take it (my stack is like a giant tanker - very slow to change direction, it takes me a long time to take a drug aboard, and a lot of evidence to make a change). YMMV.
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Have you tried bleach baths (small amt of bleach in bath for a.few m8nutes). Cleared it up.fast for several i know (including me)
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Does this even address the same area? Have there been any randomized trial that have tested the drug for MACE reduction as a primary endpoint? What about as a side-effect in its other trials for other conditions?
I can’t recall a single one. Should’ve heard about it by now.
The null hypothesis: no difference.
what kind of concentration? I’m not a huge fan of bleach lol. I’m in China now and my psoriasis is almost completely in remission. must be the humidity of the summer.
I just put one ½ to 1 small cap from the bleach bottle in the bath. For just a few minutes.
do you have a target PH level?
Unfortunately, I’ve given up using Tadalifil. I’ve noticed that when I take it, my eyesight gets so blurry that I can’t even read anymore. When I stop, my vision goes back to normal. This makes it a non-starter for me.
Unfortunately, I now have a 3 year supply I don’t know what to do with! 
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Same here. Blurry vision is known side effect of Tadalafil. Had to stop and rather concentrate on NO/citrulline.
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Yes. Citrulline has no negatives AFAIK.
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I was just wondering, what’s your daily dosage? I took 2.5 mg per day. It’s okay.
thanks.
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10 mg per day. I used to take 5 mg and the effect was noticeable but less. I didn’t try 2.5 mg. I was working on my prostate, but I’ll leave that to dutasteride now.
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A video that is a few months old, but I wanted to check on its claims:
Is Cialis (Tadalafil) the Ultimate Longevity Drug?! (The Real Biohack)
I. Executive Summary
Phosphodiesterase type 5 (PDE5) inhibitors—most notably sildenafil and tadalafil—function through competitive active-site inhibition of the PDE5 isoenzyme, preventing the hydrolytic degradation of cyclic guanosine monophosphate (cGMP). The resulting accumulation of intracellular cGMP prolongs protein kinase G (PKG) activation, modulates intracellular calcium fluxes, and induces systemic smooth muscle relaxation and microvascular vasodilation. Although initially approved for pulmonary arterial hypertension (PAH) and urological indications such as erectile dysfunction (ED) and lower urinary tract symptoms secondary to benign prostatic hyperplasia (BPH), broad tissue expression of PDE5 across cardiomyocytes, vascular endothelium, skeletal muscle, and specific subcortical neural structures has generated interest in these compounds as systemic longevity agents.
In cardiovascular medicine, retrospective pharmacoepidemiologic analyses report marked risk reductions. A study of over 72,000 men with ED demonstrated an adjusted 13% reduction in major adverse cardiovascular events (MACE) and a 25% decrease in all-cause mortality among PDE5 inhibitor users (Kloner et al., 2023), with the highest exposure quartile demonstrating a 55% lower MACE rate. In chronic heart failure cohorts, a meta-analysis of 24 randomized controlled trials confirmed that sustained PDE5 inhibition improves ejection fraction, suppresses left ventricular mass index, and lowers NT-proBNP levels (Giannetta et al., 2014). However, concomitant therapy with prescription nitrate medication represents an absolute contraindication: nationwide registry data indicate that combining PDE5 inhibitors with nitrates increases all-cause mortality by 39% and myocardial infarction risk by 72% due to profound refractory hypotension (Trolle Lagerros et al., 2024).
In neurobiology, both agents cross the blood-brain barrier. Preclinical models indicate reduced amyloid accumulation, blunted neuroinflammation, and enhanced neurogenesis in the ischemic penumbra following acute stroke. Human observational datasets suggest an adjusted 18% to 47% reduction in incident Alzheimer’s disease among regular users (Adesuyan et al., 2024). Nevertheless, drug-target Mendelian randomization analyses reveal that genetically proxied PDE5 inhibition does not confer protection against Alzheimer’s disease, suggesting that observational signals are susceptible to healthy-user bias. Claims regarding skeletal muscle anabolism are similarly constrained: pilot trials show modest, transient increases in abdominal lean mass without measurable acceleration of myofibrillar protein synthesis (Aversa et al., 2017). Outside of validated cardiopulmonary and urological indications, off-label use for non-indicated life extension remains clinically unproven.
II. Insight Bullets
- Phosphodiesterase type 5 (PDE5) inhibitors block the enzymatic breakdown of cyclic guanosine monophosphate (cGMP), thereby prolonging intracellular downstream signaling.
- Elevated cytosolic cGMP levels activate protein kinase G (PKG), which mediates smooth muscle relaxation and local vascular dilation throughout multiple organ beds.
- PDE5 isoenzymes are distributed widely across vascular smooth muscle, pulmonary vasculature, cardiac myocytes, the bladder, the prostate, and specific regions of the central nervous system.
- Sildenafil received formal regulatory clearance under the brand name Revatio from Pfizer for the clinical management of pulmonary arterial hypertension.
- In pulmonary arterial hypertension, selective dilation of the pulmonary arterial bed reduces right ventricular afterload and enhances systemic exercise capacity.
- In patients diagnosed with chronic heart failure, sildenafil therapy improves alveolar-capillary gas exchange and attenuates exercise-induced pulmonary capillary fluid transudation.
- By promoting sustained vascular smooth muscle relaxation, PDE5 inhibitors systematically improve peripheral flow-mediated endothelial function.
- A retrospective database study evaluating 72,498 men with erectile dysfunction associated PDE5 inhibitor use with an adjusted 13% reduction in major adverse cardiovascular events (Kloner et al., 2023).
- The observed cardiovascular risk reduction exhibited a dose-response gradient, with the highest-exposure quartile showing a 55% lower incidence of major adverse cardiac events (Kloner et al., 2023).
- Observational database analyses cannot establish biological causality due to confounding factors, including socioeconomic differences and healthy-user bias.
- In cohorts with heart failure with reduced ejection fraction and secondary pulmonary hypertension, continuous PDE5 inhibition improves hemodynamic parameters.
- A systematic meta-analysis of 24 randomized controlled trials confirmed that continuous PDE5 inhibitor therapy reduces left ventricular mass and circulating NT-proBNP concentrations (Giannetta et al., 2014).
- Co-administration of PDE5 inhibitors with prescription nitrate medication is contraindicated due to synergistic accumulation of cGMP triggering profound, life-threatening hypotension.
- Prescribers mandate a minimum 24-hour clearance window for sildenafil and a 48-hour window for tadalafil before administering therapeutic nitrates.
- A Swedish nationwide registry analysis revealed that combining PDE5 inhibitors with prescription nitrate medication correlates with a 39% increase in all-cause mortality and a 72% increase in myocardial infarction (Trolle Lagerros et al., 2024).
- In patients who do not require nitrate pharmacotherapy, randomized clinical trials demonstrate that PDE5 inhibitors possess a favorable cardiovascular safety profile.
- The Princeton IV Consensus Guidelines provide a clinical algorithm to stratify cardiovascular risk before initiating PDE5 inhibitor therapy.
- Within the central nervous system, PDE5 isoenzymes are localized in the hippocampus, the cerebellar cortex, and the substantia nigra.
- Both sildenafil and tadalafil effectively cross the blood-brain barrier into brain parenchyma.
- A preclinical meta-analysis across 34 animal models demonstrated that PDE5 inhibitors reduce neuroinflammation, lower oxidative stress markers, and attenuate amyloid-beta accumulation.
- A UK electronic health record cohort study reported an adjusted 18% lower hazard of incident Alzheimer’s disease among men prescribed PDE5 inhibitors (Adesuyan et al., 2024).
- Pooled observational meta-analyses across international cohorts estimate up to a 47% reduction in Alzheimer’s disease risk among regular PDE5 inhibitor recipients.
- There are currently no completed human randomized controlled trials confirming that PDE5 inhibitors prevent, delay, or treat Alzheimer’s disease.
- In animal models of acute ischemic stroke, administering PDE5 inhibitors within 24 hours of arterial occlusion promoted neurogenesis and functional penumbral reperfusion.
- Increased microvascular cGMP signaling promotes capillary recruitment and perfusion across peripheral skeletal muscle tissue beds.
- A pilot clinical trial in 43 non-obese men demonstrated that 5 mg daily tadalafil for two months increased abdominal lean tissue mass on DEXA imaging (Aversa et al., 2017).
- Measured gains in abdominal lean tissue mass returned completely to baseline values following a two-month therapeutic washout (Aversa et al., 2017).
- Cell culture experiments indicate that tadalafil exposure upregulates androgen receptor expression and myogenin transcription in myogenic cell lines.
- Online claims asserting that PDE5 inhibitors double skeletal muscle protein synthesis in humans lack clinical trial verification.
- Tadalafil is FDA-approved under the trade name Cialis by Eli Lilly at a dose of 5 mg daily for lower urinary tract symptoms secondary to benign prostatic hyperplasia.
- The therapeutic mechanism of tadalafil in benign prostatic hyperplasia involves relaxing smooth muscle tone within the bladder neck, prostate stroma, and prostatic urethra.
- Multiple Phase III randomized controlled trials confirm that daily 5 mg tadalafil monotherapy significantly improves International Prostate Symptom Scores.
- A Cochrane systematic review found that PDE5 inhibitors reduce pain severity and urinary symptoms in patients diagnosed with chronic prostatitis and chronic pelvic pain syndrome (Franco et al., 2020).
- Common adverse effects of PDE5 inhibitors include headache, facial flushing, dyspepsia, and nasal congestion secondary to peripheral vasodilation.
- Prescribers must assess renal and hepatic clearance parameters prior to initiating daily PDE5 inhibitor regimens in older adults.
III. Adversarial Claims & Evidence Table
| Claim from Video | Speaker’s Evidence | Scientific Reality (Current Data) | Evidence Grade (A-E) | Verdict |
|---|---|---|---|---|
| PDE5 inhibitors reduce major adverse cardiovascular events (MACE) by 13% to 55%. | Retrospective US insurance database study of >72,000 men with erectile dysfunction. | Retrospective data confirm lower MACE (HR 0.87) and lower all-cause mortality (HR 0.75) with highest-dose exposure reaching HR 0.45 (Kloner et al., 2023). However, residual confounding, socioeconomic stratification, and healthy-user bias limit causal inference in the absence of prospective cardiovascular outcome trials. | Level C | Plausible |
| PDE5 inhibitors reverse pathologic cardiac remodeling in heart failure. | Meta-analysis of 24 randomized controlled trials in cardiac disease cohorts. | Meta-analysis confirms significant reduction in left ventricular mass index (-12.2 g/m²), improved ejection fraction (+3.7%), and decreased circulating NT-proBNP in continuous PDE5i trials (Giannetta et al., 2014). Benefits are localized primarily to heart failure with reduced ejection fraction and secondary pulmonary hypertension. | Level A | Strong Support |
| Combining PDE5 inhibitors with organic nitrates substantially increases mortality. | Swedish nationwide registry study demonstrating elevated mortality and infarct rates. | In a nationwide cohort of 61,487 men with prior myocardial infarction or revascularization, concomitant use of nitrates and PDE5 inhibitors was associated with significantly increased all-cause mortality (HR 1.39) and incident myocardial infarction (HR 1.72) (Trolle Lagerros et al., 2024). Synergistic cGMP accumulation causes severe arterial hypotension. | Level C | Safety Warning |
| PDE5 inhibitor use decreases human Alzheimer’s disease risk by up to 47%. | Systematic review and meta-analysis of 6 observational studies comprising >8.3 million individuals. | While observational cohorts observe an inverse hazard ratio (adjusted HR 0.82 in Adesuyan et al., 2024), drug-target Mendelian randomization analyses using genetically proxied PDE5 inhibition demonstrate no protective effect against Alzheimer’s disease (OR 1.00, p = 0.96) (PMC12686590). The observational signal is largely explained by healthy-user bias and ascertainment artifacts. | Level C (Observational) / Level D (Translational Gap) | Speculative |
| PDE5 inhibitors enhance stroke recovery and penumbral neurogenesis. | Preclinical meta-analysis of 34 animal studies and animal stroke models (>3,600 animals). | Animal models demonstrate reduced apoptosis and accelerated angiogenesis within the ischemic penumbra when dosed within 24 hours. However, human randomized trials evaluating functional neurorecovery post-stroke remain small, exploratory, and clinically inconclusive (Webb et al., 2024). | Level D (Translational Gap) | Speculative |
| Tadalafil builds skeletal muscle and increases lean body mass. | Small trial of 43 non-obese men showing increased abdominal lean mass on DEXA. | A 2-month open-label trial of 5 mg daily tadalafil demonstrated a modest increase in abdominal lean mass, which reversed entirely upon drug cessation (Aversa et al., 2017). Total body fat-free mass was unchanged, and clinical trials show zero evidence of elevated myofibrillar protein synthesis. Online claims of doubling muscle growth are unsupported. | Level B (Small Trial) | Unsupported |
| Tadalafil improves urinary symptoms and pelvic pain in BPH and CP/CPPS. | FDA approval for BPH and a Cochrane systematic review in chronic prostatitis. | Daily tadalafil (5 mg) is FDA-approved for BPH, with systematic reviews showing consistent 2- to 3-point reductions in IPSS (Oelke et al., 2012). A Cochrane systematic review confirms significant symptom score and pain improvements in chronic pelvic pain syndrome (Franco et al., 2020). | Level A | Strong Support |
IV. Actionable Protocol (Prioritized)
High Confidence Tier (Level A/B Evidence)
| Domain | Clinical Action | Dosing / Target | Primary Endpoint |
|---|---|---|---|
| Benign Prostatic Hyperplasia (BPH) | Administer daily low-dose tadalafil monotherapy for lower urinary tract symptoms | 5 mg orally once daily without regard to meals (Oelke et al., 2012) | Statistically significant reduction in total International Prostate Symptom Score (IPSS ≥3-point drop) |
| Pulmonary Arterial Hypertension (PAH) | Deploy selective pulmonary vasodilators under cardiopulmonary specialist supervision | Sildenafil 20 mg TID (Revatio) or Tadalafil 40 mg once daily (Adcirca) (Galie et al., 2015) | Reduction in pulmonary vascular resistance, attenuation of right ventricular strain, and improvement in 6MWD |
| Left Ventricular Remodeling | Deploy sustained PDE5 inhibition in stable HFrEF with secondary pulmonary hypertension | Sildenafil titrated up to 50 mg TID under cardiology supervision (Giannetta et al., 2014) | Decreased left ventricular mass index, improved left ventricular ejection fraction, and reduction in circulating NT-proBNP |
Experimental Tier (Level C/D Evidence - High Safety Margin)
- Endothelial Flow-Mediated Vasodilation: Tadalafil prescribed at 2.5–5.0 mg orally once daily. Mechanistically, sustained low-level cGMP elevation enhances basal nitric oxide bioavailability, reduces endothelin-1-mediated vasoconstriction, and lowers peripheral vascular resistance (Aversa et al., 2017). Clinical monitoring includes baseline seated blood pressure, orthostatic vitals, and renal function panels (serum creatinine, eGFR).
- Chronic Prostatitis / Chronic Pelvic Pain Syndrome (CP/CPPS): Tadalafil administered at 5 mg orally once daily for a structured 12-week trial. The proposed mechanism involves downregulating local neurogenic inflammation and relaxing pelvic floor hypertonicity (Franco et al., 2020). Clinical monitoring requires logging the NIH Chronic Prostatitis Symptom Index (NIH-CPSI) and screening for post-void residual volume.
- Cerebrovascular Perfusion Optimization: Off-label daily low-dose tadalafil (2.5–5.0 mg daily). Mechanistically, this targets cerebral microvascular endothelial function, increases cerebral blood flow, and enhances neurovascular coupling via subcortical cGMP/PKG signaling (Webb et al., 2024). Clinical monitoring requires surveillance for visual symptoms (non-arteritic anterior ischemic optic neuropathy [NAION]), auditory changes, and serial cognitive evaluations.
Red Flag Zone (Debunked, High-Risk, or Contraindicated)
Concurrent Co-Administration with Organic Nitrates or sGC Stimulators: Prescribing or consuming PDE5 inhibitors concurrently with organic nitrates (e.g., nitroglycerin sublingual tablets, isosorbide mononitrate, isosorbide dinitrate) or soluble guanylyl cyclase stimulators (riociguat). Co-administration induces synergistic, uncontrolled intracellular cGMP amplification, resulting in precipitous arterial vasodilation, coronary hypoperfusion, myocardial infarction, and fatal cardiovascular collapse (Trolle Lagerros et al., 2024). A strict washout period of at least 24 hours for sildenafil and 48 hours for tadalafil is mandatory prior to nitrate administration.
Supra-Therapeutic Off-Label Dosing for Skeletal Muscle Hypertrophy: Ingesting escalated doses of PDE5 inhibitors (e.g., >20 mg/day tadalafil or >100 mg/day sildenafil) under the assumption that it stimulates myofibrillar protein synthesis. Human trials confirm that PDE5 inhibition does not alter fractional synthetic rates of muscle protein. Escalating dosages introduces significant clinical risks of priapism, severe reflex tachycardia, post-exercise hypotension, and autonomic syncope.
Empirical Monotherapy for Primary Alzheimer’s Prevention in Asymptomatic Individuals: Initiating long-term PDE5 inhibitor therapy solely for neuroprotection in cognitive normality. Mendelian randomization demonstrates that genetically proxied PDE5 inhibition does not reduce Alzheimer’s disease risk. Exposing patients to chronic pharmacological vasodilation in the absence of validated indications incurs drug cost and adverse event risk without proven neurodegenerative efficacy.
Produced by Gemini 2.5 Flash
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Are we to assume that other drugs/supplements (i.e. Arginine, NAD+ boosters etc…) that have similar effects as nitrates would have the same result, meaning it’s a big NO to combining them with PDE5 inhibitors?
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From Google Gemini 3.8 Flash, Thinking Level High:
No, it is incorrect to assume that nutritional compounds supporting the nitric oxide (NO) pathway or cellular energetics carry the same lethal contraindication as prescription organic nitrates (medications). Conflating these agents stems from a failure to differentiate between unregulated, exogenous NO donation and rate-limited, endogenous substrate kinetics.
Combining phosphodiesterase type 5 (PDE5) inhibitors with organic nitrates is contraindicated because of exponential, unbuffered cyclic guanosine monophosphate (cGMP) accumulation. Dietary supplements and metabolic precursors interact with vascular physiology through distinct molecular pathways that do not replicate this catastrophic pharmacology.
1. Prescription Nitrates vs. PDE5 Inhibitors (The Fatal Mechanism)
Prescription nitrates (such as sublingual nitroglycerin, isosorbide mononitrate, and isosorbide dinitrate) are pharmacological prodrugs. When metabolized—predominantly by mitochondrial aldehyde dehydrogenase-2 (ALDH2)—they release high concentrations of free nitric oxide directly into the vascular wall:
- Bypasses Endogenous Regulation: This delivery operates completely independent of cellular feedback loops or endothelial nitric oxide synthase (eNOS) control.
- Massive sGC Stimulation: The resulting NO flood binds to soluble guanylyl cyclase (sGC), accelerating the synthesis of cGMP from GTP.
- Refractory Hemodynamic Collapse: Under concurrent PDE5 inhibition, the primary enzymatic breakdown route for cGMP is blocked. Intracellular cGMP rises exponentially, triggering unrestrained calcium clearance from vascular smooth muscle cells, systemic arteriolar dilation, profound venous pooling, precipitous drop in mean arterial pressure, coronary hypoperfusion, and fatal myocardial ischemia.
A similarly absolute contraindication exists for direct soluble guanylyl cyclase (sGC) stimulators (e.g., riociguat, vericiguat), which also hyper-amplify cGMP synthesis independent of endogenous eNOS regulation.
2. Endogenous Amino Acid Precursors (L-Arginine and L-Citrulline)
Verdict: Not a contraindicated “big NO.” Mild additive vasodilation; safe in normotensive individuals.
L-Arginine serves as the direct physiological nitrogen donor for eNOS, while L-Citrulline acts as an efficient systemic prodrug that bypasses first-pass hepatic metabolism and is converted into L-arginine in the kidneys.
- Enzymatic Rate-Limiting Gate: Supplementing these amino acids does not cause unregulated NO synthesis. eNOS activity is strictly constrained by enzyme saturation ($V_{\max}$), intracellular cofactor availability (tetrahydrobiopterin, $\text{BH}_4$), caveolin-1 binding, and phosphorylation status (e.g., Ser1177 vs. Thr495). You cannot force an intact enzyme to exceed its kinetic ceiling simply by providing excess substrate.
- Clinical Trial Reality: Randomized controlled trials have investigated the combination of daily low-dose tadalafil (5 mg) and L-citrulline (1,500–3,000 mg/day) in patients with erectile dysfunction refractory to monotherapy. The combination demonstrates modest therapeutic synergy and improves endothelial flow-mediated dilation with only a clinically negligible, well-tolerated drop in systemic blood pressure (typically 2 to 5 mmHg systolic).
- Clinical Nuance: In individuals already taking multiple prescription antihypertensives or those with baseline orthostatic hypotension, adding high-dose citrulline to a PDE5 inhibitor can theoretically provoke transient dizziness, but it does not cause refractory circulatory collapse.
3. Inorganic Dietary Nitrates (Beetroot Juice / Nitrate Salts)
Verdict: Cautionary territory; additive hypotensive effect, but not equivalent to organic nitrates.
Inorganic nitrate ($\text{NO}_3^-$) found in concentrated beetroot extracts or nitrate salts utilizes the enterosalivary nitrate–nitrite–NO pathway:
- Mechanism: Commensal oral anaerobic bacteria reduce nitrate to nitrite ($\text{NO}_2^-$), which is subsequently reduced to bioactive NO in the acidic gastric lumen and by systemic deoxygenated hemoglobin, myoglobin, and xanthine oxidoreductase in peripheral tissues.
- Clinical Reality: Unlike amino acids, the reduction of nitrite to NO accelerates under tissue hypoxia and lower pH, partially bypassing eNOS. Human trials show that high-dose beetroot extract (supplying 400–800 mg inorganic nitrate) combined with PDE5 inhibitors generates a measurable, additive drop in systolic blood pressure of approximately 5 to 10 mmHg.
- Verdict: While healthy individuals clear this without adverse sequelae, combining supraphysiological boluses of inorganic nitrate extracts with maximum on-demand PDE5 inhibitor doses (e.g., 20 mg tadalafil or 100 mg sildenafil) introduces a risk of symptomatic hypotension in volume-depleted or clinically frail populations.
4. NAD+ Precursors (NMN, Nicotinamide Riboside, Niacin)
Verdict: Mechanistically irrelevant to the nitrate–PDE5 inhibitor contraindication. Zero cross-reaction.
Compounds that augment nicotinamide adenine dinucleotide (NAD+) pools—such as Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR)—operate through metabolic salvaging:
- Distinct Molecular Cascade: NAD+ serves as a central hydride-transfer coenzyme for mitochondrial ATP production and a rate-limiting substrate for sirtuins (SIRT1–7) and poly(ADP-ribose) polymerases (PARPs).
- Absence of Direct NO Generation: NAD+ boosters do not act as direct NO donors, do not bind to sGC, and do not drive acute cGMP production. Over chronic timelines, SIRT1 deacetylates eNOS to support baseline endothelial health, but it does not trigger acute, short-term vasodilatory surges.
- The “Niacin Flush” Distinction: High-dose nicotinic acid (immediate-release niacin) produces intense cutaneous flushing. However, this is mediated entirely through epidermal Langerhans cells via the G-protein coupled receptor GPR109A (HCAR2), triggering prostaglandin release ($\text{PGD}_2$ and $\text{PGE}_2$). It is not driven by the nitric oxide–sGC–cGMP axis. While taking high-dose flushing niacin simultaneously with a PDE5 inhibitor might compound cutaneous flushing and mild lightheadedness, it does not induce the fatal cGMP-driven collapse seen with nitrates.
Practical Risk Stratification
| Compound Class | Primary Mechanism | Interaction with PDE5 Inhibitors | Clinical Recommendation |
|---|---|---|---|
| Organic Nitrates (Nitroglycerin, Isosorbide) | Direct, non-enzymatic NO donation | Catastrophic cGMP accumulation; profound cardiovascular collapse | Absolute Contraindication. Minimum 24h (sildenafil) to 48h (tadalafil) washout. |
| sGC Stimulators (Riociguat, Vericiguat) | Direct enzymatic activation of sGC | Synergistic cGMP synthesis; refractory hypotension | Absolute Contraindication. |
| Inorganic Nitrates (Beetroot juice >400 mg) | Enterosalivary $\text{NO}_3^- \rightarrow \text{NO}_2^- \rightarrow \text{NO}$ | Additive blood pressure reduction (5–10 mmHg drop) | Moderate Caution. Avoid concurrent bolus dosing if baseline BP < 100/60 mmHg. |
| Amino Acid Precursors (L-Citrulline, L-Arginine) | eNOS enzymatic substrate | Mild additive vasodilation limited by eNOS kinetics ($V_{\max}$) | Clinically Acceptable. Monitor vitals if co-prescribed with antihypertensives. |
| NAD+ Boosters (NR, NMN) | Sirtuin / Redox cofactor biology | No direct interaction with cGMP/sGC signaling | Safe. No hemodynamic cross-reactivity. |
The clinical rule is straightforward: Do not conflate direct pharmacological NO donors with rate-limited biological substrates or redox cofactors. The absolute contraindication applies strictly to compounds that supply exogenous NO or stimulate sGC independently of cellular feedback. Supplements that support the endogenous eNOS cycle or bolster NAD+ pools operate under physiological constraints that prevent acute, lethal vascular collapse.
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Thanks, great to know.
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Been on daily 5 mg tadalafil as my urologist recommended for veins and heart past 4 years. The other benefits rock too!
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I’m unable to use it due to it’s negative effects on my eyesight.