September 16, 2026 
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William "Wes" Alden, MD, PhD | Clinical Education Series
NAD: History, Forms, Routes, and Clinical Use
By William “Wes” Alden, MD, PhD
NAD, or nicotinamide adenine dinucleotide, sits at the center of how cells make energy and manage stress. Levels tend to fall with age, and that observation has driven a wave of interest in raising them again through diet, supplements, or infusions. The underlying biology is solid. The leap from that biology to proven treatments for aging, fatigue, addiction, or cognitive decline is still incomplete for most of the claims you see online.
This article walks through the history, the main chemical forms in use today, the different ways people take them, and what the evidence actually supports.
A short history
Researchers first noticed NAD in the early 1900s while studying fermentation. By the 1930s and 1940s its structure was worked out and its role in moving electrons around the cell became clear. Around the same time, doctors recognized that pellagra (the disease of dermatitis, diarrhea, dementia, and death) responded to nicotinic acid, one of the simple forms of vitamin B3. That finding showed that the body needs a steady supply of precursors to keep NAD pools filled.
Later work mapped the pathways that build NAD from tryptophan or recycle it from nicotinamide and related compounds. Scientists also discovered that NAD is more than a redox cofactor. Enzymes such as the sirtuins and the PARPs consume it while they repair DNA or adjust gene expression. In the last two decades, papers showing age-related drops in NAD, together with experiments in animals, turned the molecule into a popular target for aging research. Companies then developed nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) as supplements, and clinics began offering intravenous NAD.
The main forms people use
NAD exists in an oxidized form (NAD+) and a reduced form (NADH). Most strategies try to enlarge the overall pool rather than deliver large amounts of the finished dinucleotide, which does not absorb well when swallowed.
Nicotinic acid (niacin)
This is the classic form of vitamin B3. The body converts it to NAD through the Preiss-Handler pathway. High doses can improve cholesterol numbers, but flushing and other side effects are common. Prescription niacin remains FDA-approved for certain lipid disorders.
Nicotinamide (niacinamide)
The amide version of B3. It feeds the salvage pathway and is widely used in skin creams for barrier support and mild anti-inflammatory effects. At very high doses it can interfere with some of the enzymes that use NAD, so more is not always better.
Nicotinamide riboside (NR)
A newer form that cells convert first to NMN and then to NAD+. Several human trials show it can raise NAD-related markers in blood. It is sold as a dietary supplement, not as an approved drug for aging or disease treatment.
Nicotinamide mononucleotide (NMN)
The immediate precursor to NAD+ in the main salvage route. Oral NMN also raises NAD metabolites in people. Large trials that measure hard clinical outcomes are still limited. Its regulatory status in the United States has shifted over time; it is generally treated as a research or supplement ingredient rather than an approved medication.
NADH and direct NAD+
Oral NADH is marketed for energy and focus, but the amount that actually reaches cells and changes the NAD+/NADH ratio is modest. Sterile NAD+ solutions are compounded for intravenous or sometimes intramuscular use in certain clinics. These preparations are not FDA-approved for the wellness, addiction, or anti-aging purposes for which they are often given.
How people take them
By mouth
This is the route used in almost every controlled trial of NR and NMN. Absorption varies with the specific compound, the dose, and the person. Blood levels of NAD-related molecules rise, yet the size of the rise inside different tissues is harder to measure.
Intravenous
Some clinics offer slow NAD+ infusions that last several hours. Rapid delivery often causes chest pressure, flushing, or nausea, so the drip is kept deliberately slow. Supporters claim benefits for addiction recovery, fatigue, and mental clarity. The published evidence is mostly small, open-label, or anecdotal. Intravenous NAD+ is not an FDA-approved treatment for those conditions. Any infusion carries risks of infection, reaction, and blood-pressure changes and should be done only with pharmaceutical-grade material under medical supervision.
Intramuscular and topical
Intramuscular injection is less common and has even less supporting data. Topical nicotinamide is a standard ingredient in dermatology for barrier repair and certain pigment problems. Creams that contain NAD+ itself are sold for skin aging, but the evidence that they raise skin NAD levels or outperform plain nicotinamide is thin.
What the evidence supports
Clear uses include preventing and treating niacin deficiency, using prescription niacin for selected lipid problems, and applying topical nicotinamide for skin conditions. Oral NR and NMN reliably change NAD metabolomics and have early data on metabolic markers and physical performance. Everything else (IV NAD for addiction or anti-aging, broad cognitive enhancement, treatment of chronic fatigue or neurodegeneration) rests on much weaker evidence. Plausible mechanisms exist, but large, well-controlled trials showing lasting clinical benefit are still missing.
Safety notes
Ordinary doses of the vitamin forms have long safety records. High-dose niacin needs monitoring for liver strain and glucose changes. NR and NMN have looked tolerable in the trials published so far, though long-term data in large groups are still being collected. Parenteral NAD adds the usual risks of any intravenous therapy. Material sold strictly for research should never be injected or infused into people.
Practical takeaway
NAD biology is real and worth understanding. Raising NAD with oral precursors can be discussed in selected metabolic situations where data exist. Expansive claims for intravenous protocols or anti-aging cures go well beyond the current evidence. The basics that support the same pathways (exercise, decent sleep, blood-pressure and glucose control, limited alcohol) still do most of the heavy lifting.
William “Wes” Alden, MD, PhD, is a physician-scientist and internist. His career has included academic medicine, federal clinical research, community practice, and medical philanthropy. He works in the Greater New Orleans area, including Metairie, New Orleans, and the Northshore communities of Mandeville and Covington. His interests include metabolic health, integrative approaches, neurodegenerative conditions, and practical whole-person care. He emphasizes honest evidence and clear communication with patients and families.
This article is for general education and reflects Dr. Alden’s professional perspective. It is not medical advice and does not create a doctor-patient relationship. Results vary from person to person. Many peptides, NAD products, and specialty lipids mentioned here are not FDA-approved for anti-aging, cognitive enhancement, or most of the wellness uses sometimes promoted. Material labeled for research use only should never be given to people. Please consult a qualified clinician about your own situation before starting any evaluation or treatment.
