The main drawback to NMN is a lack of long-term studies in humans. NMN has been shown to be safe in doses up to 1200 mg daily for 6 weeks and 900 mg daily for 8 weeks. Doses of 2000 mg daily have been taken for up to 14 days with no adverse effects.[1] Long-term safety of chronic and/or higher doses of NMN hasn’t been tested.
It is also important to note that more research is needed to better-understand the effects of boosting NAD+ in certain contexts. For example, by elevating cellular NAD+ levels, NMN could potentially exacerbate chronic inflammation by increasing the release of pro-inflammatory cytokines from senescent cells.[2] It is important to note, however, that NMN-induced inflammation has not been observed in human trials to date.