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Normally, I think it would probably be fine to mention taking such a dietary supplement in order to explain any alleged reaction(s) to drug-related questions.
However, in your particular case, since you've mentioned the specific supplement and the timing of your polygraph examination on this public message board, I think it would be unwise to mention your use of Andro to your polygrapher. If he or she reads this message board, then he/she is likely to identify you, and you are likely to be arbitrarily accused of deception and/or countermeasure use.
I am taking a poly next weekend for a local PD for employment and I have a drug question and how it might be scored. I have never touched any illegal drugs my whole life. Just something I never wanted to get involved with. ANyhow, 2 years ago I started taking a supplement for weight training, known as andro. Andro is legal all around, but after taking it I read the back of the bottle, and it stated something like- Do not take this product if you are subject to doping control procedures with the NCAA and some other kind of orgs. When I think about the drug use question, I think of Andro, it being legal and all, still makes me think of it becausae of the warning on the back.
Am I worrying too much over something that I shouldn't? Should I disclose this to the polygrapher, or will he spin that out of control?