Key Takeaways

• Delivery method matters: Oral, subcutaneous, intramuscular, and intravenous routes differ in bioavailability, absorption speed, convenience, and risk. 
• Subcutaneous vs. intramuscular injections: Subcutaneous is slow, steady, and easier for self-use; intramuscular is faster, allows larger doses, and usually requires a medical professional due to higher risk.
• Sterility and quality are essential: Only pharmaceutical-grade NAD+ from validated sterile sources should be used—this is non-negotiable. 
• Compounding pharmacies matter: Consumers should verify that their NAD+ injections come from FDA-registered 503B facilities—or, at a minimum, from 503A pharmacies with validated sterile production processes.
• Be informed: Consult a healthcare provider, verify sterility and quality, carefully follow instructions, and prioritize education to stay safe.

In recent years, nicotinamide adenine dinucleotide (NAD+) interventions have moved from niche clinical settings into the mainstream wellness landscape. Following the rise of NAD+ intravenous (IV) therapies offered by clinics and medical spas, injectable forms of NAD+ have also gained visibility as a more convenient alternative to infusions. 

This shift coincides with a broader normalization of self-injection. The widespread use of glucagon-like peptide-1 (GLP-1) medications, alongside increasing interest in peptide therapies marketed for hormonal balance and “biohacking,” has made at-home injections more familiar to consumers. What was once largely confined to insulin users or fertility treatment is now a routine practice for a growing segment of the population. 

Media interest has further amplified interest in NAD+, often framing injectable formulations as a tool to support energy levels, healthy aging, or cellular repair. Despite this growing popularity, it is important to emphasize that there is currently no published clinical evidence demonstrating the safety, efficacy, or clinical benefit of NAD+ administered via subcutaneous or intramuscular injection.

This article provides a foundational, evidence-based overview of NAD+ injections, examining what these injections are, how subcutaneous and intramuscular delivery differ in terms of absorption and practicality, and what is currently known about their safety.

What Are NAD+ Injections and How Do They Work? 

NAD+ is a critical coenzyme involved in cellular energy production, mitochondrial function, DNA repair, and cellular signaling.¹ NAD+ levels naturally decline with age and may be further reduced by metabolic stress, poor diet, and certain disease states.² These declines have driven interest in strategies aimed at increasing NAD+ levels, including injectable formulations.

Injections are a method of delivering compounds or medications directly into the body using a needle and syringe. Like IV infusions, injections bypass the digestive system and avoid first-pass metabolism in the liver, a process that can significantly reduce the amount of an orally administered compound that reaches systemic circulation. By avoiding the gastrointestinal tract, injectable delivery can result in faster and more direct absorption into the bloodstream compared to oral dosing.

Injectable administration is commonly used for compounds that are unstable, poorly absorbed, or easily degraded in the stomach or small intestine. Bypassing the gut via injection or IV infusion allows the compound to enter circulation without undergoing digestive degradation.

However, not all injections function the same way. The specific route of administration—such as subcutaneous or intramuscular injection—can significantly influence absorption rate, bioavailability, duration of effect, and practical considerations for use. These differences are particularly relevant when evaluating NAD+ injections and are explored in the following sections.

Subcutaneous vs. Intramuscular NAD+ Injections: What’s the Difference?

Injectable therapies can be administered using different techniques depending on the properties of the compound, the desired absorption, and the depth of the tissue targeted. The route of administration affects how quickly a substance enters circulation, how long its effects may last, and how practical it is to administer in at-home settings. 

The main types of injections are subcutaneous (SC, also called sub-Q) and intramuscular (IM). Each approach involves distinct anatomical targets, injection techniques, and absorption characteristics, and each is associated with different practical and safety considerations. 

Subcutaneous Injections: How They Work, Advantages, and Bioavailability 

Subcutaneous (SC) injections deliver a compound or medication into the layer of fat located just beneath the skin, but above the underlying muscle. Because this tissue contains relatively few blood vessels, compounds administered subcutaneously are absorbed more slowly and steadily into systemic circulation.

This slow, sustained release makes SC injections particularly suitable for medications or compounds that benefit from controlled absorption over time, such as insulin or GLP-1 analogues.

The most common SC injection sites include the abdomen (typically at least two inches away from the navel), the outer upper arms, the front or outer thighs, and the upper buttocks or lower back. For therapies requiring repeated injections—such as insulin—rotating injection sites is generally recommended to reduce the risk of tissue damage, irritation, or lipohypertrophy (localized fat lumps).

Advantages of subcutaneous injections include:

• Relatively steady absorption 
• More predictable systemic exposure compared to oral routes 
• Easier self-administration in home settings
• Reduced pain (compared with deeper, intramuscular injections)
• Lower risk of inadvertently hitting blood vessels 

In terms of bioavailability, SC injections generally provide greater systemic exposure than oral administration, as the compound bypasses the digestive tract and first-pass metabolism in the liver. However, absorption is slower than with IM or IV delivery. 

Intramuscular Injections: How They Work, Advantages, and Bioavailability 

Intramuscular (IM) injections are delivered directly into muscle tissue, which is much more vascularized (has more blood vessels) than subcutaneous fat. The richer blood supply in muscle allows compounds to be absorbed more rapidly into systemic circulation compared with SC injections. This faster absorption can result in a quicker onset of effects and generally higher bioavailability than SC administration. 

Common IM injection sites include the deltoid muscle in the upper arm, the vastus lateralis in the thigh, and the gluteal muscles in the buttocks. IM injections can accommodate larger volumes than subcutaneous injections, making them suitable for compounds or medications that require higher doses or faster systemic exposure.

Advantages of intramuscular injections include:

• Faster onset of action, compared to SC injection
• Greater and more predictable bioavailability 
• Can accommodate larger doses 
• Suitable for compounds that require rapid systemic effects, such as certain hormonal therapies

However, while IM injections can be self-administered in some cases, they are typically performed by healthcare professionals to reduce the risk of nerve injury, tissue damage, or improper administration. IM injections are also generally more painful than SC injections due to delivery into muscle tissue, and may cause temporary soreness or muscle stiffness afterward, similar to vaccines.

Table 1. Comparison of Subcutaneous and Intramuscular NAD+ Injection Methods

 

Bioavailability and Pharmacokinetics of Injections Compared to Other Delivery Methods

Bioavailability refers to the proportion of a substance that reaches the bloodstream in active form, while pharmacokinetics describes how the body absorbs, distributes, metabolizes, and eliminates a substance. These concepts are key to understanding why different delivery methods—such as subcutaneous (SC), intramuscular (IM), intravenous (IV), and oral routes—produce different systemic exposures and onset times.

• Subcutaneous Injections: Provide moderate-to-high bioavailability, with absorption that is generally slow and steady due to the relatively low vascularization of subcutaneous fat. This allows compounds to enter circulation gradually, which can be advantageous for medications or supplements intended for sustained release.
• Intramuscular Injections: Offer higher bioavailability and faster onset of action. Muscle tissue contains a richer network of blood vessels than subcutaneous fat, allowing compounds to be absorbed more quickly into systemic circulation. IM injections also accommodate larger volumes, which can be useful for certain therapies.
• Intravenous Infusions: IV infusions are considered the benchmark for bioavailability, delivering 100% of the substance directly into circulation. This method produces immediate systemic exposure and bypasses all absorption barriers.
• Oral Supplementation: Oral routes generally result in lower bioavailability. Compounds taken by mouth are subject to degradation in the gastrointestinal tract and first-pass metabolism in the liver, which reduces the amount that reaches systemic circulation in an active form. While taking NAD+ orally has not been shown to raise systemic NAD+ levels, precursors like nicotinamide riboside (NR) are proven to increase NAD+ in humans.

Overall, no single method is inherently “better” or “worse” than another. The choice of administration method depends on practical considerations, including the desired speed of absorption, the properties and volume of the compound, convenience, and patient comfort.

Preparation, Reconstitution, and Administration of NAD+ Injections

NAD+ injections are often supplied as lyophilized (freeze-dried) sterile powder that requires reconstitution with a sterile diluent, such as bacteriostatic water, prior to administration. Proper reconstitution, accurate dosing, and adherence to safety protocols are essential responsibilities for anyone administering injections, whether in a clinical setting or at home. This means that if you self-inject, you are responsible for safely reconstituting and measuring the dose.

Compared with IV infusions, injections provide a faster and more flexible delivery option, allowing administration outside of multi-hour clinic sessions on your own time. SC injections are easier to self-administer, making them more suitable for at-home use. IM injections, on the other hand, carry a higher risk of tissue or nerve injury, which is why they are typically performed by healthcare professionals.

NAD+ injections are often compounded in specialized pharmacies, which adhere to the same strict sterility and quality standards applied in IV therapies. This ensures that the injections are prepared under controlled conditions to minimize contamination and maintain product integrity.

Compounding, Sterility, and Safety Considerations for NAD+ Injections

Safe and proper compounding of NAD+ injections is critical because these products bypass the digestive system and enter the bloodstream directly. To ensure sterility, accuracy, and pharmaceutical-grade quality, NAD+ injections are typically prepared in specialized compounding pharmacies.

Pharmaceutical-grade compounds meet strict purity, potency, and quality standards suitable for injection, unlike food-grade or supplement-grade ingredients, which may not meet sterility requirements. Using pharmaceutical-grade NAD+ produced in compounding pharmacies helps minimize the risk of contamination or adverse reactions.

Compounding pharmacies produce medications that are not commercially available or require customization. In the U.S., they fall into two categories:

• 503A compounding pharmacies prepare medications for individual patients based on prescriptions, regulated primarily by state boards, and must comply with safety standards such as USP 797. They are limited in bulk production and typically have shorter beyond-use dates.
• 503B outsourcing facilities are FDA-registered, can produce sterile medications in bulk for clinics and hospitals, and must follow Current Good Manufacturing Practices (cGMP) with validated sterility and environmental controls.

This distinction matters for NAD+ injections because any contamination, formulation inconsistency, or dosing variability can pose serious clinical risks. Injections bypass the gut, so contamination with microbes or endotoxins can cause infections or systemic reactions. Notably, the FDA has issued warnings and classified recent NAD+ injection recalls as Class I or Class II due to endotoxin contamination and non-sterility concerns, respectively.

For safe and reliable injectable (or IV) NAD+ therapy, products should come from FDA-registered 503B facilities—or, at a minimum, from 503A pharmacies with validated sterile production processes. For a detailed breakdown of compounding pharmacies, FDA oversight, and safety protocols, see our article on IV NAD+ therapy. 

How to Ensure Your NAD+ Injections Are Safe

For anyone considering NAD+ injection therapy—whether at home or in a clinical setting—adhering to rigorous safety practices is essential. Use this checklist to guide your evaluation and decision-making:

• Consult a healthcare provider first: Seek professional guidance on proper self-administration techniques, dosing, and monitoring.
• Confirm pharmaceutical-grade and sterile NAD+: Only use pharmaceutical-grade NAD+ intended for injection, produced under validated sterile conditions.
• Request documentation: Ask for a certificate of analysis (COA) or batch testing summary demonstrating sterility, potency, and endotoxin testing.
• Verify sterile supplies and procedures: Ensure all needles, syringes, and diluents are sterile, and proper reconstitution techniques are followed.
• Follow storage instructions: Proper refrigeration or handling is crucial to maintain product stability and safety.
• Educate yourself: Carefully read and adhere to all instructions to reduce the risk of contamination, dosing errors, or adverse reactions.

For a more detailed discussion of sterility, quality, and safety considerations—including an in-depth checklist—see our article on IV NAD+ therapy. 

Conclusion: Making Informed Decisions About NAD+ Injections

NAD+ injections have emerged as a convenient alternative to IV infusions, offering a faster and more direct way to support NAD+ levels than oral routes. Each delivery method—oral, SC, IM, or IV—differs in bioavailability, absorption speed, practicality, and risk. Oral supplementation is familiar and convenient for long-term support but is subject to digestive degradation and first-pass metabolism. Conversely, injections and IV therapy may provide more immediate and potent increases in systemic NAD+, although clinical studies confirming their efficacy are lacking.

Between the two injection routes, SC injections deliver NAD+ into the fat layer beneath the skin, providing slow, steady absorption and ease of self-administration. IM injections deliver NAD+ into muscle tissue, allowing faster systemic uptake and accommodating larger volumes, but are typically administered by healthcare professionals due to a higher risk of tissue or nerve injury.

Regardless of the route, sterility and quality control are non-negotiable. NAD+ injections must be pharmaceutical-grade and prepared under validated sterile conditions. FDA-classified recalls highlight the dangers of non-sterile or improperly compounded products. Consumers should verify that their injections come from compliant compounding pharmacies—either FDA-registered 503B facilities or, at a minimum, 503A pharmacies with validated sterile production processes.

Ultimately, informed decision-making is paramount. Consumers should carefully vet providers and products, request safety and sterility documentation, follow storage and administration instructions, and prioritize education and adherence to sterile-compounding standards. By doing so, individuals can maximize safety while exploring NAD+ injections as part of a broader strategy for supporting cellular health and energy metabolism.

 

References

1. Rajman, L., Chwalek, K., & Sinclair, D. A. (2018). Therapeutic Potential of NAD-Boosting Molecules: The In Vivo Evidence. Cell Metabolism, 27(3), 529–547. https://doi.org/10.1016/j.cmet.2018.02.011
2. Massudi, H., Grant, R., Braidy, N., Guest, J., Farnsworth, B., & Guillemin, G. J. (2012). Age-Associated Changes In Oxidative Stress and NAD+ Metabolism In Human Tissue. PLoS ONE, 7(7), e42357. https://doi.org/10.1371/journal.pone.0042357