NR vs NMN vs Nicotinamide for Glaucoma: Which NAD+ Booster Has the Strongest Evidence?

NAD⁺ and Glaucoma: Why Vitamin B₃ Matters

Glaucoma is an aging-related eye disease in which retinal ganglion cells (RGCs) – the nerve cells that carry visual signals from the eye to the brain – gradually die off. Pressure-lowering treatments (drops, lasers, surgery) are the standard of care, but many patients still experience slow vision loss. Researchers have therefore been exploring additional neuroprotection strategies. One promising idea is boosting NAD⁺ (nicotinamide adenine dinucleotide) – a vital cell energy molecule – because NAD⁺ levels naturally decline with age (pmc.ncbi.nlm.nih.gov). Lower NAD⁺ may leave RGCs less able to meet their high energy needs, especially under glaucoma stress. In fact, one lab review notes that “glaucoma is a neurodegenerative disease in which neuronal levels of NAD decline,” and shows that nicotinamide (vitamin B₃) can protect RGCs in multiple animal glaucoma models (pmc.ncbi.nlm.nih.gov). This finding has inspired human trials of NAD-boosting supplements in glaucoma.

Current research has focused on three NAD precursors: nicotinamide (vitamin B₃), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN). All three are natural forms of B₃ that feed into the NAD⁺ salvage pathway (pmc.ncbi.nlm.nih.gov). Nicotinamide (often called niacinamide) is a form of vitamin B₃ found in foods and multivitamins; NR and NMN are specialized NAD precursors found in small amounts in some foods (and sold as supplements). But do they really help glaucoma? Below we compare what is known about each one in plain language. All claims below are backed by recent science and trials.

Nicotinamide for Glaucoma

Why is nicotinamide being studied?

Researchers study nicotinamide because it directly boosts NAD⁺ via the cell’s salvage pathway and has strong lab evidence in glaucoma models. In aging cells, NAD⁺ “declines with age at a systemic level” (pmc.ncbi.nlm.nih.gov). RGCs are very energy-hungry cells in a high-stress environment (high pressure can damage mitochondria inside them). Boosting NAD⁺ could supercharge RGC metabolism and help them survive. In rodent glaucoma experiments, high-dose nicotinamide dramatically protected RGC bodies and axons. For example, Tribble et al. (2021) report that dietary nicotinamide blocked the early metabolic disruptions caused by high eye pressure and improved mitochondrial function in rat retinas (pmc.ncbi.nlm.nih.gov). In simple terms, vitamin B₃ helped the energy cells in the retina keep working properly under stress. This strong preclinical data has given researchers confidence to try nicotinamide in human glaucoma.

Human trial evidence for nicotinamide

Human studies are still small but encouraging. A 2022 trial in open-angle glaucoma (with moderate field loss) gave patients high-dose nicotinamide plus another agent (pyruvate). Participants took 1–3 grams of nicotinamide daily. Over ~2 months, the treatment group showed significantly more improvement in visual field test points than placebo did (pubmed.ncbi.nlm.nih.gov). Specifically, the median number of improved field locations was 15 in the nicotinamide group versus 7 in placebo (p=0.005) (pubmed.ncbi.nlm.nih.gov). Secondary measures of field sensitivity also tended to improve more with treatment. Although this trial was short and combined with pyruvate, it provides a positive signal that NAD boosting can help glaucoma (and importantly, no serious side effects were reported (pubmed.ncbi.nlm.nih.gov)).

Another recent trial focused on normal-tension glaucoma (a form of glaucoma without high eye pressure). Korean researchers gave 1.5–3.0 grams of nicotinamide daily to patients already on pressure-lowering drops. Over 12 weeks, they found measurable improvements in inner retinal function using specialized tests (the Photopic Negative Response in an electroretinogram) (pmc.ncbi.nlm.nih.gov). In plain terms, injured retinal neurons worked better after taking nicotinamide. Most patients tolerated the doses well. This trial did not show changes in standard visual field tests, but the early functional recovery is promising (pmc.ncbi.nlm.nih.gov).

Safety data so far are reassuring with proper medical supervision. Nicotinamide (unlike niacin) does not cause facial flushing. Mild side effects at several grams may include nausea, headache or dizziness, especially if taken without food (pmc.ncbi.nlm.nih.gov). Very high doses (above 6–9 grams per day) have been linked to reversible liver enzyme elevations (pmc.ncbi.nlm.nih.gov), which is why trials generally use 1–3 grams. Importantly, no serious adverse events were seen in the glaucoma studies above (pubmed.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). (In other fields, nicotinamide has a decade of human use: for example, it is being studied to prevent skin cancers and has a favorable safety profile in those trials (pmc.ncbi.nlm.nih.gov).)

Overall, nicotinamide has the strongest evidence so far in glaucoma because of its proven lab effect on RGCs and some positive clinical signals. Ongoing studies (including larger Phase II/III trials) will tell us more about visual benefits and optimal dosing.

Comparing NAD⁺ Boosters: Nicotinamide vs. NR vs. NMN

All three compounds raise NAD⁺ but enter the pathway differently:

• Nicotinamide: This is vitamin B₃ in amide form. In cells it is converted by the enzyme NAMPT into NMN, then by NMNAT enzymes into NAD⁺ (pmc.ncbi.nlm.nih.gov). Thus nicotinamide needs two steps (NAMPT then NMNAT) to become NAD. It also very quickly turns into NAD if given in high doses, but it can compete with other NAD-related pathways (for example, high nicotinamide can inhibit sirtuin enzymes that use NAD). At normal nutritional doses it’s simply a vitamin; at high doses it floods the NAD pathway.

• Nicotinamide Riboside (NR): This is another form of B₃ that cells can use. NR first converts into NMN by NR kinases (NRK enzymes), then into NAD by NMNAT (pmc.ncbi.nlm.nih.gov). In other words, NR also takes two steps (NRK then NMNAT), but the first step is different from nicotinamide’s. The advantage is that NR does not rely on NAMPT and does not raise nicotinamide levels, so it may avoid some feedback inhibition and methyl-donor demand. In practice, NR is well-absorbed orally and has been shown in human trials to dose-dependently raise blood NAD⁺ with few side effects (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

• Nicotinamide Mononucleotide (NMN): This compound sits just one step away from NAD. NMN is normally produced inside cells from nicotinamide, but it can also be taken up (with help). NMN directly converts to NAD via NMNAT (one step) (pmc.ncbi.nlm.nih.gov). This suggests NMN is one chemical step closer to NAD than NR or nicotinamide. However, whether orally taken NMN efficiently enters the eye/retina is debated. A specialized transporter for NMN (Slc12a8) was identified in mouse intestine (pmc.ncbi.nlm.nih.gov), but its relevance in humans isn’t fully clear. In summary, NMN could theoretically boost NAD faster, but it is not as well-validated in human nutrition.

Cost and availability: Nicotinamide is extremely cheap (it’s sold as generic vitamin B₃). NR supplements (brand name Niagen, etc.) are much more expensive per dose. NMN is also costly and is not currently approved for supplements in some regions. For example, Europe classifies NMN as a “novel food,” so it cannot legally be marketed there as a supplement (www.klartext-nahrungsergaenzung.de). (In the US, NMN supplements recently became allowed, but NR and nicotinamide have long been standard nutraceuticals.) In practical terms, nicotinamide tablets are widely available over-the-counter, whereas NR and NMN are sold as specialized, high-cost supplements.

Why Choose Nicotinamide in Trials?

Clinical trials so far have focused on nicotinamide for several reasons. First, nicotinamide has decades of safety data as a vitamin supplement, making regulators comfortable with higher doses. Second, the preclinical glaucoma studies used nicotinamide, so there was a direct rationale to translate that into humans (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Third, nicotinamide is cheap and easy to dose uniformly in trials. In contrast, NR/NMN are newer molecules: they had to be produced under more stringent conditions and until recently had limited human data. Only now are trials (like NCT06991712) being planned to compare NR, NMN, and nicotinamide head-to-head in glaucoma patients (clinicaltrials.gov). In short, researchers “start with what works”: since nicotinamide already showed glaucoma benefits in animals, it makes sense to test it first in people.

Evidence for NR and NMN in Glaucoma

Nicotinamide Riboside (NR)

As of 2025, there have been no published human glaucoma trials of NR. All evidence comes from lab studies. These animal studies are promising but must be interpreted with caution. For instance, one rat model of chronic eye pressure (glaucoma) showed that feeding NR (1000 mg/kg/day orally) for three weeks increased retinal NAD⁺ levels and preserved RGC axons (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Similarly, a mouse study used a combination of acute optic nerve injury and chronic microbead glaucoma models: it found that systemic NR treatment significantly preserved RGC survival and visual function (www.mdpi.com). Collectively, these animal experiments demonstrate that NR can protect RGCs under stress. They argue that NR is bioavailable and well tolerated in rodents, and “may support the proposition of prospective human studies” (www.mdpi.com).

There is also evidence that orally giving NR to healthy humans safely raises NAD⁺. In clinical trials of overweight adults, NR (in doses up to 1000 mg/day) doubled blood NAD⁺ without causing flushing or serious side effects (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). NR supplementation did not increase homocysteine (a possible risk of NAD precursors) according to one study (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Thus, NR appears very safe even at high doses. The bottom line: no direct glaucoma trials yet, but animal results suggest NR could help glaucoma in theory, and human safety data are strong.

Nicotinamide Mononucleotide (NMN)

Human glaucoma studies of NMN do not yet exist. NMN has some evidence in other eye contexts. For example, in a retinal detachment model (photoreceptor injury), NMN treatment increased retinal NAD and reduced cell death (www.aging-us.com). However, that is a different part of the retina (photoreceptors) and a different injury. In the context of glaucoma (RGC injury), no published study has tested NMN in animals or humans yet. Therefore, any benefit of NMN in glaucoma is purely theoretical at this point.

We do know some things about NMN from general research: In healthy adult trials (for aging), NMN up to 900 mg daily was found to safely boost blood NAD⁺ without adverse events (pmc.ncbi.nlm.nih.gov). In the 60-day dose-ranging trial of 300–900 mg/day, “no NMN-related adverse events and dropouts” occurred (pmc.ncbi.nlm.nih.gov). But whether NMN taken by mouth actually reaches retinal cells in glaucoma patients is an open question.

Theoretical Pros and Cons

• Could NR or NMN be better than nicotinamide? It’s possible in theory. NR and NMN bypass the early NAMPT step, which some believe is a bottleneck in aging. They may raise NAD more directly without creating excess nicotinamide (which uses up methyl groups). Animal studies suggest NR tasks cells in different ways (for example, via AMPK pathways (pmc.ncbi.nlm.nih.gov)). If NR or NMN delivery to the eye is efficient, they might more strongly boost NAD inside RGCs. However, this is speculative. Importantly, raising blood NAD (as NR and NMN can do) does not guarantee retinal NAD increase, due to tissue uptake differences. In early comparative studies, equimolar doses of NR, NMN and nicotinamide are being tested in glaucoma patients (clinicaltrials.gov) exactly because nobody knows which will work best.

• Could nicotinamide be better? On the other hand, nicotinamide has practical advantages. It has decades of safety and a well-known pharmacology. It is cheapest and most stable to formulate. Nicotinamide is also readily converted into NAD in tissues; some data suggest that in the eye it is quickly taken up to replenish NAD stores. In fact, nicotinamide was found to restore NAD in the injured retina in animal glaucoma models (pmc.ncbi.nlm.nih.gov). So far, only nicotinamide has clear positive signals in human glaucoma. Researchers value this “trial-first” evidence. Thus, none of the NAD boosters has a definitive home-run advantage yet; nicotinamide’s practical track record makes it a leading choice in current trials.

Safety Concerns of NAD Boosters

While NAD boosters are generally safe when used appropriately, there are important precautions:

• Liver and metabolism: High-dose nicotinamide (above ~6 grams per day) has been associated with reversible liver enzyme elevations (pmc.ncbi.nlm.nih.gov). In skin cancer trials, doses of 9–10 g/day caused hepatitis in some patients (pmc.ncbi.nlm.nih.gov). For glaucoma, trials use more moderate doses (1–3 g/day). Even so, patients should take nicotinamide with food and under doctor supervision if using multi-gram doses. NR and NMN so far at doses up to 1 g/day have shown no liver toxicity in trials (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). However, long-term safety (years) is still unknown.

• Methylation and homocysteine: Nicotinamide is methylated in the body (to N-methylnicotinamide), which uses up the methyl-donor SAM. Very high nicotinamide intakes could in theory deplete methyl donors and raise homocysteine, a vascular risk factor. Indeed, a single 300 mg dose of nicotinamide was shown to acutely raise plasma homocysteine (pmc.ncbi.nlm.nih.gov). By contrast, NR in human trials did not raise homocysteine (pmc.ncbi.nlm.nih.gov), likely because it bypasses the same methylation pathway. NMN’s effect on homocysteine is less studied, but it eventually also feeds into the same NAD pool, so moderation is wise. Patients taking high doses may consider B vitamins (B6/B12/folate) to support methyl metabolism, as is sometimes recommended by integrative physicians.

• Other effects: NR and NMN do not cause the flushing or itching that niacin (nicotinic acid) does. No effects on blood sugar or lipids have been seen at studied doses (pmc.ncbi.nlm.nih.gov). Rare reports in industry suggest some people may experience mild nausea or headaches early on, but these resolved or were no different from placebo rates (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

• Drug interactions: NAD boosters could theoretically interact with medications by altering metabolism enzymes, but no known clinically important interactions have been reported. As with any supplement, it is safest to discuss with your eye doctor or pharmacist, especially if you take multiple medications.

Bottom line: NAD precursor supplements appear low-risk at typical doses, but very high intakes should be approached cautiously. Always inform your physician before self-dosing vitamin B₃ at gram levels.

What Glaucoma Patients Should Take Away

• Clinical evidence: To date, nicotinamide (vitamin B₃) has the strongest glaucoma-specific evidence. Its benefits have been seen in animal studies and very small human trials of RGC function (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). In contrast, nicotinamide riboside and NMN remain mostly theoretical for glaucoma. There are promising animal studies for NR (www.mdpi.com) (pmc.ncbi.nlm.nih.gov), but no published human trial results yet. NMN has no direct glaucoma data yet (just some lab studies in other eye models (www.aging-us.com)).

• No replacement for standard care: Importantly, none of these supplements should replace your prescribed glaucoma treatments. Controlling eye pressure, using your drops, having regular field tests and OCT scans are the evidence-based ways to slow vision loss. NAD boosters can be considered additional strategies, but only with doctor guidance. Until large clinical trials show clear benefits on vision or field loss, we should regard nicotinamide/NR/NMN as experimental/developmental.

• Dosage and safety: If considering nicotinamide, current research uses roughly 1–3 grams per day (divided doses). Lower doses (e.g. a typical multivitamin) are far below what’s studied. Always talk to your doctor about any high-dose vitamin regimen, because your health history (liver issues, diabetes, etc.) matters. Nicotinamide is water-soluble, so any excess is excreted, but large doses can still affect metabolism. Avoid self-prescribing megadoses without supervision. Similarly, NR or NMN supplements (if you have access to them) should be used cautiously and ideally under study conditions for now.

• Summary of evidence: In simple terms, nicotinamide (vitamin B3) is currently the front-runner for glaucoma neuroprotection. It has a real biological rationale and some early human data. NR and NMN are scientifically interesting NAD boosters, but for glaucoma their use is still unproven – basically, we hope they might work based on basic science, and bigger clinical trials are needed to see if that hope pans out.

• Continue standard monitoring: Don’t skip your regular glaucoma check-ups. NAD boosters, even if helpful, would only add a modest protective effect. Your main defenses remain lowering eye pressure when needed, taking prescribed drops faithfully, and monitoring your visual fields and retinal nerve health with your ophthalmologist. View any NAD booster as a possible “extra credit” strategy rather than a primary therapy.

Comparison of NAD⁺ Precursors for Glaucoma

Conclusion

In summary, nicotinamide (vitamin B₃) currently has the strongest case in glaucoma of the three NAD⁺ boosters. Its role in RGC metabolism is well-grounded, and small human studies hint at functional benefit (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). NR and NMN are promising in theory and show neuroprotective effects in animals (www.mdpi.com) (pmc.ncbi.nlm.nih.gov), but they lack direct human glaucoma evidence. Future trials (including the ongoing ones) will clarify whether these newer boosters help patients. For now, glaucoma patients should not abandon proven treatments. If considering any NAD⁺ supplement, discuss it with your eye doctor. Remember that lowering intraocular pressure, following prescriptions, and regular monitoring (fields, OCT) remain the top priorities for protecting vision.

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Sources: Recent reviews and clinical studies on NAD⁺ metabolism and glaucoma (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) (www.mdpi.com) (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).