Let’s be clear about this. It has been the case since 1987. The results of polygraph tests are unreliable and risky. Police still use polygraph tests, not for the results but rather to put you through a process to set you up for a post-test interrogation when they tell you that you failed the test in order to obtain a confession, false or otherwise. Simple rule –> do NOT take a polygraph test.
Source: Can evidence of a polygraph test be used in court? | Provincial Court of British Columbia