The unknown drug is likely to be:

Ans. (B) High dose AdrenalineGiven figure shows that after giving a drug, blood pressure first increases and then decreases. It is known as biphasic response which is characteristic of high dose adrenaline. At low doses, adrenaline stimulates only beta 2 receptors and thus cause only fall in BP. But at high doses, it stimulates both alpha and beta receptors and initially cause rise in BP due to alpha receptor stimulation, however as plasma concentration falls, it lead to decrease in BP due to stimulation of only beta 2 receptors. This is known as biphasic response