NAD+ (nicotinamide adenine dinucleotide) has gone from obscure biochemistry term to wellness industry buzzword in about five years. IV drip clinics, injectable formulations, oral supplements — the market is flooded with products promising to restore youthful NAD+ levels.

Some of the science is genuinely exciting. Some of the marketing has gotten way ahead of the evidence. Here's an honest look at both.

What NAD+ Actually Does

NAD+ is a coenzyme found in every living cell. It's involved in over 500 enzymatic reactions and plays a central role in two critical processes:

1. Energy metabolism

NAD+ is essential for converting food into cellular energy (ATP). It shuttles electrons in the metabolic pathways that power your mitochondria. Without adequate NAD+, your cells literally can't produce energy efficiently.

2. DNA repair and cellular maintenance

NAD+ is consumed by enzymes called sirtuins and PARPs, which repair damaged DNA, regulate gene expression, and maintain cellular health. These are the pathways most linked to aging — and they require NAD+ as fuel.

Think of NAD+ as the currency your cells use to perform maintenance. When levels are high, maintenance runs smoothly. When levels drop, things start to degrade.

The Age-Related Decline

NAD+ levels decline with age. This isn't controversial — it's well-documented across multiple studies and tissues. The commonly cited figure is approximately 50% reduction by age 40 compared to age 20, though the exact rate varies by tissue type and measurement method.

The decline appears to result from both increased consumption (more DNA damage to repair as we age) and decreased production (the biosynthetic pathways become less efficient). It's a double hit.

This decline correlates with many hallmarks of aging: mitochondrial dysfunction, increased inflammation, impaired DNA repair, metabolic slowdown. The question is whether restoring NAD+ levels can meaningfully reverse or slow these processes in humans.

The Best Clinical Evidence

The Lancet Healthy Longevity RCT (2024)

This randomized, double-blind, placebo-controlled trial — published in one of medicine's most prestigious journals — tested oral NMN (a NAD+ precursor) supplementation in middle-aged and older adults. Participants who received NMN showed increased NAD+ levels in blood and improvements in walking speed (a validated biomarker of biological aging). It was one of the first well-designed human RCTs to show functional improvement from NAD+ boosting.

The NADPARK Study

This clinical trial investigated NAD+ replenishment in Parkinson's disease patients using NR (nicotinamide riboside). The study found that NR supplementation increased brain NAD+ levels and was associated with mild clinical improvements, though the study was small and results were described as preliminary.

Preclinical evidence

The animal data is much stronger. Studies in mice have shown NAD+ replenishment improving mitochondrial function, extending lifespan in certain models, improving insulin sensitivity, and reducing age-related decline across multiple organ systems. These results are exciting but the translation to humans remains unclear.

Injection vs Oral vs IV

Subcutaneous injection

Bypasses the digestive system. The NAD+ or its precursor enters the bloodstream directly. Higher bioavailability than oral. This is the route most telehealth peptide providers offer. Typical protocols use NAD+ or NMN injections 2-5 times per week.

Oral supplements (NMN, NR)

More convenient but lower bioavailability. NAD+ itself is poorly absorbed orally, which is why precursors like NMN and NR are used — they're absorbed and then converted to NAD+ in the body. The Lancet RCT used oral NMN and showed meaningful results, so oral isn't ineffective — it may just require higher doses.

IV infusion

The "drip clinic" approach. High-dose NAD+ delivered directly into the bloodstream over 2-4 hours. Produces the most dramatic acute effects (often described as a rush of mental clarity and energy, though the infusion itself can cause nausea, chest tightness, and cramping). Expensive ($500-1500 per session) and time-consuming.

The Honest Assessment

What's well-established:
- NAD+ levels decline significantly with age
- NAD+ is critical for energy metabolism and DNA repair
- Supplementation can raise blood NAD+ levels
- Animal data strongly suggests benefits from NAD+ restoration

What's promising but still developing:
- Whether NAD+ restoration produces clinically meaningful improvements in human aging
- The optimal route, dose, and frequency for supplementation
- Long-term safety data for chronic supplementation
- Which specific age-related conditions benefit most

What's overstated:
- Claims of dramatic anti-aging effects in humans (the evidence isn't there yet)
- "Reverse your biological age" marketing
- Comparisons to fountain-of-youth or miracle cures

NAD+ science is legitimate and evolving. The biology is sound, the animal data is compelling, and early human trials are encouraging. But we're at the beginning of understanding how to translate this into reliable human benefits. Anyone selling certainty is selling ahead of the science.