RecruitingPhase 1Drug trialRandomized, Open-label, Safety Study of Subcutaneous and Intramuscular Injections of Niagen® PlusThe goal of this study is to learn about the safety of Niagen®Plus, an injectable form of nicotinamide riboside (NR), and to see how it affects levels of NAD+ in the blood. Niagen®Plus will be given either by subcutaneous (under the skin) or intramuscular (into the muscle) injection at two dose levels (50 mg or 100 mg). The main questions this study aims to answer are: Is Niagen®Plus safe and well-tolerated when given by injection several times over 100 days? How do NAD+ levels in blood change after repeated doses of Niagen®Plus? What are participants' and clinicians' experiences with the injections? Researchers will also look at changes in fatigue, sleep, quality of life, inflammation markers, mitochondrial efficiency, and perceived skin appearance. Participants will: Receive three injections in clinic on Days 1-3, followed by a Day 10 follow-up visit Self-inject Niagen®Plus at home three times per week from Days 10-100 Return to the clinic on Days 40 and 100 for safety and laboratory testing Complete short surveys about fatigue, sleep, and overall well-being throughout the study The study will include 40 generally healthy adults and will last about 100 days per participant.