I am supposed to take a polygraph exam sometime later this year and have heard from others that I will not be permitted to take medications before the exam. Is this usual for a polygraph or have I been misinformed? They are for maintaining bp, pulse, depression, and bipolar disorder. Would discontinuing them for the time before the exam adversely effect the results? And can I legally be compelled to do so by other than a medical doctor?

one

You are misinformed.  Take all meds as directed by your doctor.

Anyone who would tell someone to not take medications as directed by a doctor should be hit upside the head with a tack hammer.  If it was a polygraph examiner who told you this he should have his license burned.

Always take your medications as directed by your doctor.  Drugs do not change the outcome of a polygraph.  Drugs affect your physiology from the x to the xx of a polygraph, in other words, it changes things as a baseline level.  A good polygraph examiner looks for changes in your baseline that are timely, significant and consistent, or at least most of us do.

Take your meds and go into the room with the truth.  I wish you well in your polygraph experience.