My HormonologyUsually have trust in others? You may become less trusting or doubt folks’ intentions during Week 2 of your cycle (which starts 8 days after the first day of your period) due to high testosterone, according to a study out of the University of Cape Town, South Africa. Though testosterone is widely known for boosting aggression, researcher Jack van Honk, Ph.D. explains it’s a hormone that also prompts us to become more dominant and want to rise higher in our social rank. To that end, testosterone may make us more watchful and wary of others and better prepared to defend our resources and status.