Absorption and Tolerability of Injectable Administration of Niagen®+, as Compared to NAD+

Inclusion Criteria: * Provision of signed and dated informed consent form * Stated willingness and demonstrated ability to comply with all study procedures, as well as availability for the duration of the study * Lives within 100 miles of the NRI study site * Any gender, aged 40-65, inclusive * Good general health as evidenced by medical history * BMI 25-34.9 kg/m2 * Sedentary behavior (defined as \<20 minutes per day or 100 minutes per week of moderate to vigorous exercise) * Demonstrated fatigue (Fatigue Assessment Scale) defined as a below-average score * For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation and for an additional month after the end of the study * Agreement to adhere to Lifestyle Considerations throughout study duration Exclusion Criteria: * Current diagnosis of any seizure disorder, diabetes or insulin resistance, any kidney or liver disorder, heart disease, anemia, cancer, or Parkinson's disease * ANY chronic illness (pre-disease state acceptable) * Out of range phosphate levels at baseline * BMI less than 25 or greater than or equal to 35 * Pregnancy, trying to conceive, or breastfeeding * Known allergic reactions to any components of the intervention or related compounds, including any form of B3 * Positive COVID-19 test within 30 days of the study period * Recent dramatic weight changes (10% change in body weight in the last 6 months) * Existing usage of a NAD+ or NAD precursor supplement in any form (oral, nasal, patch, or injection/IV administration), including a B-complex supplement, within 60 days of the study, not including multivitamins. * Introducing a new medication, supplement, investigational drug, or other intervention (including lifestyle changes) within 60 days of the start of the study.