Here's the short version. Nobody has run a trial that times how fast NAD+ injections make healthy people feel better. The few human studies of NAD+ given by vein measured blood levels or, in one heart-failure trial, heart function [2] [3]. So "you'll feel it in a week" is a clinic's experience, not a study result.
What has actually been measured
Human studies of NAD+ given by vein have measured blood levels and, in one heart-failure trial, heart function. None measured energy or aging.
A 2026 PRISMA-guided review searched human and rodent studies from January 2010 to October 2025 and found 113 that qualified. It found no outcome trials of intravenous or intramuscular NAD+ for anti-aging or wellness. The one IV NAD+ study it found was a pharmacokinetic pilot with no clinical outcomes [4]. The first author owns a company that manages an aesthetics clinic; the review says that clinic doesn't offer NAD+.
| Study | Who | Design, size | Route and length | What was measured | Result |
|---|---|---|---|---|---|
| Grant 2019 [2] | Small group of adults | Pilot: 8 NAD+, 3 saline controls | IV, one 6-hour infusion | NAD+ and its breakdown products in plasma and urine | Plasma NAD+ unchanged for the first 2 hours; NAD+ and methylnicotinamide up in urine by 6 hours. Some authors list an NAD+ research company and a wellness center as affiliations |
| Yu 2026 [3] | 180 adults with heart failure from ischemic cardiomyopathy | Randomized, placebo-controlled, one center | IV, 7 days, alongside standard heart-failure drugs | Ejection fraction at 1 month; major heart and stroke events at 6 months | Ejection fraction 45.44% vs 42.44% on placebo (p = 0.024); 6-month events 14.6% vs 24.7% (p = 0.089, not significant) |
| Gallagher 2026 [4] | 113 studies (33 human) | Systematic review | Not applicable | Outcome trials of injected or IV NAD+ for wellness | None found |
Why blood NAD+ may not jump right away
In the infusion study, plasma NAD+ didn't change for the first 2 hours. Meanwhile NAD+ and its breakdown products showed up in urine by 6 hours [2].
The authors' reading: infused NAD+ was "rapidly and completely removed from the plasma for at least the first 2 h," and the pattern fit enzymes breaking it down [2]. That's one small pilot with only three saline controls. It does tell you that "more NAD+ in your blood within minutes" isn't something the human data show.
Disclosure that matters here: several authors list affiliations with NAD+ Research and Springfield Wellness Center [2]. A study run partly by people in the NAD+ business isn't wrong for that reason, but it's worth knowing when you weigh it.
A 2026 retrospective clinic review reported gastrointestinal symptoms, increased heart rate and chest pressure during NAD+ infusions. It evaluated short-term tolerability, not randomized wellness efficacy; employees of the commercial provider authored it [1].
Don't mix up NAD+ injections with NMN or NR pills
Studies showing blood NAD rising within weeks used oral precursors such as NMN, not NAD+ injections, and those results don't transfer.
In one example, 80 healthy middle-aged adults took NMN or a placebo for 60 days. Blood NAD was higher in every NMN group at day 30 and day 60 [5]. Three authors are employees of Abinopharm and ABA Chemicals, so read it as industry-run. The 2026 review sums up the precursor trials the same way: they reliably raise NAD-related markers, but effects on how people function were mixed and often null [4].
NMN is a different molecule taken a different way. A clinic that quotes NMN timelines for NAD+ shots is borrowing someone else's data.
The one randomized trial of IV NAD+
In 180 adults with ischemic heart failure, a 7-day IV NAD+ course plus standard care gave an ejection fraction of 45.4% vs 42.4% on placebo at 1 month. Major events at 6 months weren't significantly different [3].
That's a real, measured change, in a single center, in people with damaged hearts. It isn't a wellness result, and it doesn't tell you anything about energy in healthy adults. The NT-proBNP and symptom-class trends in the trial didn't reach significance [3].
How to judge a program's "you'll feel it in X weeks"
Ask what the claim is based on. If it isn't a trial, treat it as the clinic's experience, and decide how much weight that gets.
- Ask which study the timeline comes from. A named, published trial is a good answer; "our patients report" is a different kind of answer.
- Check the population. A result in heart failure or in NMN pill-takers isn't a result for NAD+ shots in healthy people.
- Ask what happens if nothing changes, and how a plan is paused or canceled.
- Your prescriber sets the plan. Ask them what they'd expect and by when.
Programs like Strut Health, Gala and Brightmeds sell at-home NAD+ injections with a clinician review. Before paying, see what NAD+ injections cost, and how the prescription routes differ.
When to talk to your prescriber
If you feel unwell during or after an injection, or nothing changes, raise it with the prescriber who ordered it.
NAD+ isn't an FDA-approved drug. It's in Category 1 of FDA's 503A list, updated May 14, 2026, which may fall within FDA’s interim enforcement policy when all applicable conditions are met [6]. There's no FDA-reviewed label, so there's no official list of side effects or expected timelines to check against. Your prescriber is the person to ask.
If steadier energy is the goal, the energy shortlist compares programs side by side, and the 30-second match narrows it to your situation. For another "how long" question, see how long sermorelin takes to work.