The NAD-HD Study: A Study to Investigate Efficacy and Safety of Nicotinamide Riboside Compared With Placebo in Huntington's Disease

The goal of this clinical trial is to learn if oral supplement of nicotinamide riboside (NR), a form of vitamin B3, slows disease progression in adults with Huntington's disease. It will also learn about the safety of nicotinamide riboside. The main questions it aims to answer are: * Does NR slow progression of overall symptom burden in Huntington's disease? * Does NR have an effect on any specific symptom domain in Huntington's disease? * Does supplementation with NR cause side-effects or safety issues when used for 2 years in Huntington's disease? * Does NR have an effect on selected blood, imaging, and oculomotor biomarkers in Huntington's disease? Researchers will compare NR to a placebo (a look-alike substance that contains no active compound) to see if NR works to treat Huntington's disease. Participants will: * Take 2000mg NR or a placebo every day for 2 years * Visit the clinic once every 6 months for clinical investigations and tests * Undergo brain imaging at baseline and upon completion of the study period