Clinical trials studying vitamin B3 for glaucoma have used nicotinamide (also called niacinamide) at doses ranging from 1,000 to 3,000 mg per day. The most common protocol starts at 1,000 mg daily for six weeks, then increases to 1,500 or 2,000 mg daily. These doses are far above the standard dietary recommendation for vitamin B3 (16 mg for men, 14 mg for women) and are being studied specifically as a neuroprotective supplement alongside conventional glaucoma treatment, not as a replacement for it.
Dosages Used in Clinical Trials
The handful of human trials completed so far have used slightly different dosing schedules, but they cluster in the same range. A crossover trial published in the British Journal of Ophthalmology used 1,000 mg per day for the first six weeks, then stepped up to 2,000 mg per day for the following six weeks. Another randomized trial in patients with open-angle glaucoma used 1,500 mg per day for six weeks, then continued at a lower maintenance dose for another six weeks.
A separate trial at the Chinese University of Hong Kong took a different approach, testing nicotinamide riboside (a closely related form of B3) at just 300 mg per day over 24 months. That study is looking at whether a lower dose of a more bioavailable form can achieve similar results over a longer period.
No single “best dose” has been established yet. Researchers are still working out whether higher doses produce better outcomes or simply more side effects. What the trials do agree on is that the effective range appears to be well above what you’d get from diet or a standard multivitamin.
Which Form of Vitamin B3 Matters
Vitamin B3 comes in three main supplemental forms: nicotinic acid (niacin), nicotinamide (niacinamide), and nicotinamide riboside (NR). For glaucoma, nicotinamide is the form with the most research behind it. Nicotinic acid causes skin flushing and stomach irritation at high doses, which makes it impractical for the 1,000 to 2,000 mg range these trials require. Most people can’t stick with it.
Nicotinamide riboside is more efficient at raising cellular levels of the molecule that actually matters (NAD+, the energy currency your cells run on), so smaller doses may be effective. It also doesn’t interfere with certain protective enzymes called sirtuins the way nicotinamide does, which could be an advantage. Nicotinamide, on the other hand, produces a more sustained increase in NAD+ levels and has decades of safety data at high doses. For now, nicotinamide remains the most commonly recommended form because of its track record, availability, and lower cost. A direct head-to-head comparison of the two hasn’t been done yet.
How It Protects the Optic Nerve
Glaucoma damages the retinal ganglion cells, the neurons that carry visual information from your eye to your brain. These cells are energy-hungry, and their mitochondria (the structures that generate cellular energy) are among the first things to malfunction as glaucoma develops. Research in animal models has shown that NAD+ levels in the retina drop with age, and this decline leaves ganglion cells unable to cope with the added stress of elevated eye pressure.
Nicotinamide works by replenishing NAD+. In mouse models of glaucoma, oral nicotinamide prevented the formation of damaged mitochondria, reduced DNA damage, and preserved the synaptic connections between neurons. It also limited the activity of enzymes called PARPs that consume NAD+ during DNA repair, essentially stopping a vicious cycle where stressed cells burn through their remaining energy reserves trying to fix themselves. The key finding from animal research is that maintaining adequate NAD+ levels makes ganglion cells more resilient to pressure-related damage, rather than lowering eye pressure itself.
What Improvement Looks Like
In the 12-week human trial, participants taking nicotinamide showed measurable improvements in the electrical responses of their inner retina, detected by electroretinography. This is a functional test, meaning the cells were working better, not just surviving. The improvements were most pronounced in areas of the visual field that had intermediate sensitivity loss. In practical terms, the supplement appeared to be helping ganglion cells that were struggling but not yet dead.
That distinction is important. Nicotinamide doesn’t appear to resurrect cells that have already been destroyed. It seems to rescue cells in a “pre-degenerative” state, where metabolic dysfunction has set in but irreversible structural damage hasn’t occurred yet. Animal studies confirm this: the benefit is strongest when supplementation begins before or during early-stage disease. In late-stage glaucoma, the enzymes needed to convert nicotinamide into NAD+ are themselves downregulated in the optic nerve, which may limit how much benefit supplementation can provide.
Measurable changes in the human trials appeared within 6 to 12 weeks. Longer trials running 24 months are underway to determine whether these early functional improvements translate into preserved visual fields over time.
Safety at High Doses
Nicotinamide is generally well tolerated at the doses used in glaucoma trials (1,000 to 2,000 mg per day), but it’s not without risks at higher intakes. Minor side effects reported in studies include dull headaches, nausea, and dizziness. These tend to appear at the upper end of the dosing range.
More serious concerns emerge at doses of 2,000 mg and above. Two weeks of 2,000 mg daily was enough to decrease insulin sensitivity in one study, which is relevant if you have diabetes or prediabetes. Liver toxicity has been documented at 3,000 mg per day and higher, including cases of liver cell injury and bile flow problems. Kidney function also deserves attention: a breakdown product of nicotinamide is classified as a uremic toxin, meaning it can accumulate in people with impaired kidney function and potentially cause harm.
There’s also a theoretical concern about long-term high-dose use. Nicotinamide inhibits PARP enzymes, which are involved in DNA repair. While this reduces NAD+ consumption in the short term (a good thing for stressed neurons), chronically suppressing DNA repair raises questions about cancer risk over years of use. No human trial has run long enough to evaluate this conclusively.
Early-Stage vs. Advanced Glaucoma
The research consistently points toward earlier intervention producing better results. In animal models, nicotinamide preserved the branching structure of ganglion cell dendrites in a dose- and timing-dependent way, with the greatest benefit when supplementation began before eye pressure started rising. By the time structural damage to the optic nerve is advanced, the cells’ own machinery for producing NAD+ is compromised, creating a bottleneck that external supplementation may not fully overcome.
Human data aligns with this pattern. The visual field locations that improved most during nicotinamide supplementation were those with moderate, not severe, sensitivity loss. If you have early or moderate glaucoma, the existing evidence is more encouraging than if you have advanced disease, though supplementation in advanced cases hasn’t been ruled out as unhelpful.
What This Means in Practice
Nicotinamide is being studied as an add-on to standard glaucoma treatment (pressure-lowering drops, laser, or surgery), not a standalone therapy. No trial has shown that it lowers eye pressure. Its role is protective: keeping vulnerable cells alive and functional while conventional treatment addresses the pressure side of the equation.
If you’re considering supplementation, the dosing pattern supported by the most evidence is 1,000 mg of nicotinamide per day, potentially increasing to 1,500 or 2,000 mg after several weeks. The stepped approach used in trials likely exists to monitor tolerance before escalating. Given the risks to insulin sensitivity, liver, and kidneys at higher doses, blood work to monitor these systems is reasonable if you plan to supplement long-term, particularly if you have diabetes, liver disease, or reduced kidney function.