"Miraa" or Khat, is a flowering plant, the stems of which are chewed to produce a stimulating effect. Though, I did not chew it myself, the effects seem akin to taking Adderall or mild amounts of cocaine. I've been around people on all of the above and similarities are noticeable: wide-eyed, chatty, focused yet scattered, alert, stimulated, friendly.
After the initial rise, there's also a lull, contemplative period that usually takes place a couple hours into a chewing session. Though, I was reassured that this is not a "come down" like that typically experienced with a substance like cocaine. It can be introspective, but not inextricably tied to anxiety or depression. One makes plans and actually has the wherewithal to not only act on them in the future, but even during the session. A friend of mine told me of his engineering pal who would chew through the night to make project deadlines the following day. In this sense, the comparison to Adderall seems the most apt.
It is a common practice in Kenya, particularly among the Somali community, but transcends most.
There's not much of a stigma against it from what I've experienced - somewhere between cigarettes and marijuana - though there are campaigns to criminalize its use in Kenya and abroad. See www.vice.com/vice-news/khat-power