I had a hair folicle test today. They took my armpit hair. Will infrequent drug use show up?

Quite possible. They can take any hair off your body they want for a test. Armpit hair is no different.. only is slower growing and they will get a longer lookback than head hair.

It was only one 20mg adderrall about 2 weeks ago. Do you think that will show or am I safe?

You say infrequent and then you say once - armpit hair, as Smothy said, shows a longer history.

What is the total history?

What happens if you fail ?

It was for pre employment. Other than the one adderrall I took a couple weeks ago I haven't had any in 6 months and even then it was just occasional.

What job field? Some order far more comprehensive tests than others... and have higher standards for acceptable results.

It's a trucking company. All they did was the standard 5 panel required by Dot.