Black pepper (kaaraa merch) have Chromium and Chrysin compounds. Chrysin is a bioflavonoid and it is a natural aromatase-inhibitor that increases free testosterone. Therefore, pepper has libido-enhancing effect and anti anxiety properties. Chromium is trace mineral that balance the sugar in our body. Different levels of sugar/glucose in the body effects the mood, therefore, by balancing the sugar levels in the body black peppers help maintain the good mood.
I am not an expert on this or any other issues. My views on this and other issues are just my personal views and they could be wrong. 

[...] Black peppers have anti anxiety properties [...]
[...] Black peppers have anti anxiety properties [...]