As Sgramirez already explained, they are taking Cheongsimhwan, a traditional Korean herbal medicine which is considered good for anxiety and nervous states.
*Cheongsimhwan, a traditional Korean herbal medicine, is composed of about 30 different kinds of herbs. This herbal medicine is believed to promote the circulation of the peripheral blood.* font: clinical research grant from Pusan National University Hospital 2010.
Needless to say, the clinical research did not found out that the medicine is effective; it only stated that it didn't have effects. :P