NAD+ (Nicotinamide Adenine Dinucleotide) itself is a naturally occurring coenzyme found in all living cells, so it does not have “side effects” in the traditional sense when produced endogenously. However, when administered as supplements (precursors like NR or NMN) or through intravenous NAD+ therapy, some reported side effects include nausea, fatigue, headaches, abdominal discomfort, and mild flushing. High doses may occasionally cause anxiety, muscle cramps, or insomnia, particularly with IV infusions. Oral precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) are generally well tolerated, though long‑term safety data is still limited. Because NAD+ influences metabolic pathways, there is ongoing research into its effects on liver enzymes, cardiovascular health, and cancer risk, but no definitive adverse outcomes have been established. Overall, supplementation is considered safe for most individuals, though careful monitoring is recommended in clinical settings.