If you take Sildenafil (the active ingredient in Viagra) and still feel like your results are inconsistent, you're not alone, and new clinical research suggests there may be a simple, natural way to help it work better.

A study presented at a 2025 meeting of the International Society for Sexual Medicine and published in The Journal of Sexual Medicine found that combining a nitric oxide–boosting dietary supplement with Sildenafil significantly increased the strength and duration of nighttime erections compared to Sildenafil alone, and did it without any reported side effects.

The study was led by Dr. Judson Brandeis, a board-certified urologist, published clinical researcher, and the founder of AFFIRM Science.

How the Study Worked

Nitric oxide (NO) is the molecule your body uses to relax blood vessels and improve blood flow. PDE-5 inhibitors like Sildenafil work by preserving the cGMP that nitric oxide produces, which is why the two mechanisms are believed to complement each other. Until now, there's been limited objective data confirming that a nitric oxide–boosting supplement can meaningfully enhance a PDE-5 inhibitor's effect.

To find out, researchers had 22 men (average age 55, average SHIM score 18.1) complete a controlled, within-subject protocol:

• A 2-day washout period with no ejaculation, ED medications, or supplements
• Days 1–2: Sildenafil 40mg alone, taken one hour before bed
• Days 3–4: Sildenafil 40mg plus two tablets of a nitric oxide–boosting dietary supplement, also one hour before bed

Each night, participants wore the FirmTech TechRing, a wearable erection ring with built-in sensors that objectively measures the firmness, duration, and frequency of nighttime erections via an AI-powered app. Nighttime erectile activity is considered a reliable, objective marker of vascular and erectile health, since it removes the guesswork (and self-reporting bias) of daytime assessments.

The Results

The data showed a statistically significant improvement when the supplement was added to Sildenafil:

• 34% increase in nighttime erectile activity (area under the curve per hour of sleep rose from 87 to 117; p=0.00004)
• More erections per night, an average of 3.87 vs. 3.25 with Sildenafil alone (p=0.034)
• Zero self-reported side effects from either the supplement or the Sildenafil/supplement combination

The nitric oxide–boosting supplement used in the study is commercially available as AFFIRM. Each tablet contains 750mg L-Citrulline, 65mg Muira Puama Extract (4:1), 45mg Red Beet Root Extract (4:1), and 35mg Panax Ginseng Root Extract (4:1), ingredients selected for their role in nitric oxide production and blood flow support. You can review the full ingredient breakdown and clinical rationale on the AFFIRM Scientific Abstract page.

Why This Matters if You Take (or Are Considering) ED Medication

PDE-5 inhibitors are effective for many men, but a meaningful percentage experience dose-limiting side effects like headaches, flushing, or nasal congestion. The study's authors note that a nitric oxide–boosting supplement may improve genital circulation enough to enhance a PDE-5 inhibitor's effectiveness, potentially without needing to increase the medication dose. Because AFFIRM works through a different physiological pathway (increasing nitric oxide substrate) rather than blocking PDE-5, it's designed to complement, not replace, a prescription ED medication.

As always, talk to your physician before combining any supplement with a prescription medication.

Who Ran This Study?

Dr. Judson Brandeis is a board-certified urologist and sexual medicine researcher, and the author of The 21st Century Man, an award-winning men's health book. He founded AFFIRM Science to bring clinically studied, evidence-based formulas to men's sexual and vascular health, a mission that stands in contrast to the largely unregulated men's supplement market.

Disclosure: The study's authors are affiliated with AFFIRM Science and FirmTech. We believe in full transparency about that relationship, and it's exactly why the study was designed with objective, device-measured outcomes (rather than self-reported surveys) and published in a peer-reviewed journal.

Track Your Own Results

Curious how your own nighttime erectile activity compares? The same FirmTech TechRing used in this study is available for anyone who wants objective, at-home data on their sexual and vascular health, no clinic visit required.

Try the Supplement Used in the Study

Ready to see what a nitric oxide boost can do for you? Shop AFFIRM at checkout to save 10% on your first order. Want to track your own results the way this study did? The AFFIRM + TechRing Bundle pairs the exact supplement and tracking device used in the research.

Frequently Asked Questions

Is AFFIRM safe to take with Sildenafil (Viagra)?
In this study, no side effects were reported when the supplement was combined with Sildenafil 40mg. As with any supplement-medication combination, consult your healthcare provider first.

Do I need a prescription to take AFFIRM?
No. AFFIRM is an over-the-counter dietary supplement made from L-Citrulline, Red Beet Root, Panax Ginseng, and Muira Puama extracts.

What is the TechRing, and how is it different from other trackers?
The TechRing is a wearable erection ring with built-in sensors that measures the firmness and duration of erections, including nighttime erections, and syncs the data to a phone app via Bluetooth. It's the device used to generate the objective data in this study.

Where can I read the full study?
The abstract, "Combining a Nitric Oxide Boosting Dietary Supplement With Sildenafil Improves Nighttime Erections More Than Sildenafil Alone," is published in The Journal of Sexual Medicine (Oxford Academic), Volume 22, Supplement 4. Read it here.