Nasal SprayFrom $166/mo
InjectionFrom $166/mo
Medically reviewed by Vanessa Niles, R.N., M.D., F.A.C.O.G. —
Definition
Bioavailability, in plain English
Federal regulations (21 CFR 314.3) define bioavailability as the rate and extent to which a drug's active ingredient is absorbed and becomes available at the site of action. The National Cancer Institute puts it plainly: the ability of a drug to be absorbed and used by the body.
A drug given into a vein is 100% bioavailable by definition. Other routes lose some along the way.
- Measures
- How much and how fast a drug is absorbed
- IV
- 100% by definition
- Defined in
- 21 CFR 314.3
How it connects
How bioavailability relates to NAD+
NAD+ bioavailability by nasal spray or injection under the skin hasn't been well measured in people. Oral NAD+ is thought to be largely broken down in the gut, one reason precursors such as NR and NMN are studied instead.
For your treatment
What bioavailability means for NAD+ therapy
Your provider chooses a form and dose with these unknowns in mind and adjusts based on how you respond.
- Free online consultation with a licensed U.S. provider
- NAD+ nasal spray or injection, plans from $166 a month if prescribed
- NAD+ has no FDA-approved use; compounded NAD+ isn’t FDA-approved
Questions
Bioavailability: common questions
What is bioavailability?
Bioavailability is how much of a medicine, and how fast, reaches the bloodstream or the place where it acts. It differs by route: IV, injection, nasal spray or by mouth.
Which NAD+ route has the highest bioavailability?
IV, by definition. For nasal spray and injection, human data are limited.
Is oral NAD+ effective?
Oral NAD+ is thought to be largely broken down before it's absorbed; researchers more often study oral precursors such as NR and NMN.
What strengths does NADMedics prescribe?
Nasal spray: 30 mg per 0.1 mL in a 15 mL bottle. Injection: 200 mg/mL in a 5 mL vial. Your provider sets your dose.
How do I report a side effect?
Tell your provider, and you can report it to the FDA's MedWatch program. Call 911 for chest pain or trouble breathing.
Do I need a prescription for NAD+?
Yes. Compounded NAD+ requires a prescription from a licensed provider after a review of your health.
Keep learning
Related NAD+ terms
Terms that connect to bioavailability, each explained on its own page.
- Treatment & safetyNAD+ IV infusionAn NAD+ IV infusion delivers NAD+ straight into a vein through a drip, usually over several hours in a clinic. It's different from the at-home nasal spray and injections NADMedics prescribes.
- Treatment & safetySubcutaneous injectionA subcutaneous injection is a shot into the fatty layer just under the skin, usually in the belly or thigh, with a short, thin needle. It's how at-home NAD+ injections are given.
- Treatment & safetyIntranasal administrationIntranasal administration means giving a medicine as a spray into the nose, where it's absorbed through the nasal lining. It's how NAD+ nasal spray is used.
- Vitamins & precursorsNAD+ precursorAn NAD+ precursor is any molecule the body can turn into NAD+. The main ones are tryptophan, nicotinic acid, nicotinamide, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN).
Guides that cover bioavailability
Official sources
Bioavailability: sources and official resources
Official government and research sources behind this page, so you can check the facts yourself.
- Electronic Code of Federal Regulations21 CFR 314.3: Definitions (bioavailability)
The federal definition of bioavailability: the rate and extent a drug's active ingredient is absorbed.
- National Cancer InstituteNCI Dictionary of Cancer Terms: bioavailable
The ability of a drug or other substance to be absorbed and used by the body.
- Frontiers in Aging NeuroscienceGrant et al. Changes in the human NAD+ metabolome during a 6-hour NAD+ infusion (2019)
Small pilot study of intravenous NAD+ in healthy adults.
- NIH PubMed CentralCovarrubias et al. NAD+ metabolism and its roles in cellular processes during ageing (2021)
Review of how NAD+ works in cells and how levels change with age.
Medically reviewed by Dr. Vanessa Niles, R.N., M.D., F.A.C.O.G., on October 12, 2026. This glossary is general education, not medical advice. NAD+ has no FDA-approved use, and compounded NAD+ is not FDA-approved or evaluated by the FDA for safety or effectiveness. Talk with a licensed provider before starting any supplement or treatment.
Questions about NAD+? Ask a provider
Book a free online consultation. A licensed U.S. provider reviews your health and, if NAD+ fits, prescribes the nasal spray or injection, with plans from $166 a month.
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