So this post applies to the United States, where all citizens can be called to do their civic duty, and sit on a jury.
In the US, all juries, and all jursits, have the right to find someone “Not guilty”- regarless of how much evidence there is that they are gulity, for the sole reason that the law is unjust.
This was an important control given to the people to prevent unjust or immoral laws.
So, simply put, if one is on a jury for someone accused of possessing, producing, or selling marijuana or other “illegal” drugs, you, as a jurist, have the right to find them not guilty by no other basis then the law itself being unjust.
There is a gread pamphlet on the matter from writer and illustrator Ricardo Cortes available here. http://www.rmcortes.com/books/jury/Jury-Illustrated.pdf
Power to the people- and let freedom ring.
I know there are similar laws in Canada- although I believe the prosecutor has the right to appeal cases lost on the basis of jury nullification.