Kratom can act as a stimulant, as a psychedelic and as depressant .

What is a stimulant?
Stimulants are drugs that stimulate the Central Nervous System. These substances tend to increase alertness and physical activity. They include Amphetamines, Cocaine, Crack and some inhalants like Amyl or Butyl Nitrites. Caffeine (present in tea, coffee and many soft drinks) is also a mild stimulant drug.

Information about drugs: stimulants