After taking your last dose of Niacin it should be out of your system within 110mins to 247mins (2hrs to 4hrs)

Niacin has a short half-life of 20 to 45 minutes. This is the time it takes for your body to reduce plasma drug levels by half. It takes approximately 5.5 x elimination half- life for a drug to be eliminated from your system.

However other factors to consider include:
1. How much and how often you have taken the drug.
2. Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
3. Your age and health – older age and poor health will generally increase the time the drug stays in your system.
4. Body mass – generally the bigger you are the longer a drug will remain in your system.