NAD side effects depend on the route, and the three routes people use have very different records. Drips have one study of what people felt. Injections under the skin have none. Pills made from its building blocks have several randomized trials.
This page keeps them apart, because a finding for one route says little about the others. What the drips were tested for is on NAD IV therapy, and the claims made for injections on NAD+ injections. NAD+ sits under the longevity goal here.
| Route | Human safety data | What it recorded |
|---|---|---|
| IV drip of NAD+ | One records review from a commercial clinic | Stomach symptoms, faster heartbeat and chest pressure during the drip |
| Injection under the skin | None published | Not studied in people |
| Nasal spray | None published | Studied only in mice and cells |
| Oral nicotinamide riboside | Randomized trials, 4 to 12 weeks | No more side effects than placebo |
| Oral NMN | A 2026 meta-analysis of randomized trials | No rise in side effects or liver enzymes |
IV drips: symptoms during the infusion
The clearest side-effect record for NAD+ itself comes from a 2026 review of clinic records [1]. Clients received 500 mg of NAD+ by vein on four days in a row. A comparison group received the same dose of nicotinamide riboside, a building block of NAD+.
The NAD+ group reported moderate to severe stomach symptoms, a faster heartbeat and chest pressure during the infusions. All of it resolved when the drip ended. The symptoms made NAD+ drips last 97 minutes on average, against 37 minutes for the comparison drip.
Blood tests of the liver, kidneys, thyroid and inflammation did not change over 30 days. One enzyme, alkaline phosphatase, fell in the NAD+ group but stayed in the normal range. HDL cholesterol also fell in that group. The review was retrospective, with no placebo group.
Injections under the skin: not studied
Online sellers commonly prescribe NAD+ as a shot under the skin. No published study has recorded what those shots do in people, good or bad. A 2026 systematic review of NAD+ studies through October 2025 found no outcome trial of NAD+ given by vein or by injection into muscle for aging or wellness [3].
That gap is not proof the shots are safe or unsafe. It means their side effects have not been counted in a study. The nasal form has even less: its only study, covered in NAD nasal spray, was in mice and in human cells in a dish.
Oral building blocks: the best-studied route
Nicotinamide riboside and NMN are not NAD+. They are smaller molecules the body turns into NAD+, sold as supplements. Unlike NAD+ shots, they have been tested in randomized trials with placebo groups.
In an 8-week trial in overweight adults, nicotinamide riboside at 100, 300 or 1,000 mg a day raised blood NAD+ by 22%, 51% and 142% [4]. There were no reports of flushing, and side effects did not differ from placebo at any dose.
A 12-week trial gave 2,000 mg a day to 40 obese men, or placebo [5]. No serious side effects were attributed to it, and safety blood tests were normal. It also found no gain in insulin sensitivity.
The highest dose tested was 3,000 mg a day, split in two, for 4 weeks in 20 people with Parkinson’s disease (n=10 per arm) [6]. There were no moderate or severe side effects. Homocysteine, a blood marker linked to heart risk, rose slightly at first.
For NMN, a 2026 meta-analysis pooled randomized trials at 250 to 2,000 mg a day, lasting 14 days to 24 weeks [7]. NMN did not raise overall, serious or system-specific side effects, or the liver enzymes ALT and AST.
What no study has measured
Every study above ran for weeks or months, the longest about 24 weeks. Nobody has measured what years of NAD+ drips, shots or supplements do. The oral trials also used pills, so their clean safety record does not transfer to a drip or an injection.
If you are weighing a route, the side-effect record is strongest for pills and absent for shots. For how often drips are given and what they cost in time, see NAD IV therapy again, and for a separate compound often sold beside NAD+, see glutathione injections.