I am taking a hair follicle test soon as part of a drug screening for my local PD. However, at the time of the test it will have been 88 days since I ingested one 10mg Adderall XR. It is the one and only time I have ever taken it. Two months ago I had a long drive and without thinking I took it so that I would remain awake for the drive. The drug company being used is psychemedics and they state they use guidelines similar to SAMHSA. Similar labs use those guidelines which leads me to believe that the cutoff levels will be 300 pg/mg for methamphetamines. The only place I have hair long enough to cut for this 90 day test is on my leg, so I know it's coming from there. I'm also aware that hair from this part grows much slower than on my head, plus there is the 10 or so days it takes to show up in the follicle. So, I'm sure my use will be in that window. Also, my hair is brown which I believe also works against me.

My questions are: At a growth rate of .3mm of hair on the day of use and a cutoff level of 300 pg/mg, will my one time use of Adderall 10mg XR be enough to fail? Is there a formula I can use to calculate any of this? Even though the metabolites are locked in the follicle, after 2 months and regular washing does the hair deteriorate? Some of what I have read also states that there is also a percentage that is digested and excreted by the body and therefore won't make it to hair growth. Is this true?

Before just asking the internet I did want to do some research but some of what I have read is just too technical, and a lot of the other posts I have read have someone saying "it will be fine." and an immediate contradicting post that says "it will show up forever." Plus, most post authors don't share the results.