I finally found it:
What are some consequences of Khat use? v
Common side effects include anorexia, tahycardia, hypertension, insomnia, and gastric disorders.
Chronic Khat abuse can result in symptoms such as physical exhaustion, violence, and suicidal depression.
Widespread frequent use of Khat impacts productivity because it tends to reduce worker motivation.
Khat can induce manic behaviors, hyperactivity, and hallucinations.vi
There are reports of Khat-induced psychosis.vii
This may explain the violent and suicidal tendencies. Or not.
Khat users. Just who I want driving my cab.
But you bring up an interesting point. This is apparently a substance which acts like the stimulant drugs which are illegal here. It could go far to explain the irrational behavior we see and they, apparently, don't recognize in themselves.