After the first century, Bhutan acquired the name Mon Yul, and the people, Monpa.
Geographically, Bhutan is located to the south of the Himalayan range, and thus the name Lho (south) and the people, Lhopa.
In the 12th century, Tibetan physicians came to Bhutan to collect medicinal herbs, which were abundantly available. Hence, they called the country Menjong Lha'i Zhingsa.
In the 17th century, Zhabdrung Ngawang Namgyal came to Bhutan and introduced the Drukpa Kagyud tradition of Buddhism. The name of the Buddhist tradition he followed was given to the country. Therefore, the name, Druk Yul (land of thunder Dragon) and the people, Drukpa. The founder of Drukpa Kagyue School, Tshanpajarey named his school Drukpa after hearing 9 roaring sound of dragon in the sky.
Since there are many junipers growing in abundance in all parts of the country, the name Lho Tsenden Keypai Jong was also given.
Internally we call our country as Druk meaning 'Dragon' due to predominant Drukpa school of Tibetan Buddhism that is followed in the country. However externally our country name is known by Bhutan. The name 'Bhutan' appears to derive from the Sanskrit 'Bhotant' meaning 'the end of Tibet' or from 'Bhu-uttan' meaning 'high land' as seen from Indian view.
Reference: Khenpo Phuentsho Tashi