Niacin, please!

I'm sooooo nervous! I worked at the local Sam's Club last year for a good nine months. The only reason why I got the job was because I had cheated during the drug test (don't ask). Now I'm scheduled for an interview today so I can redeem my job and I'm so nervous because I might need to take another drug test! They called me literally like five minutes ago to tell me to come in today for a quick interview. I'm familiar with the fact that it is necessary to take a drug test the day of the interview and not going to the testing clinic can result in me not getting hired. I'm so freaking nervous. Does anyone know where I can get some niacin?! Well rather than me sitting here & blogging, I will go buy myself a gallon of water to get started. I'll update you guys later!