Out in the desert wastes of my planet, there are living multiple tribes of psychotic raiders who have acquired a number of harmful mutations due to naturally high radiation in the areas that they live. Years of exposure and inbreeding in each individual tribe have made these mutations much more severe, and as a result the raiders have short life spans, weak immune systems, and often times diminished intelligence. The only positive part is that they are usually very large and physically powerful, partially due to genetics and partially due to their rough lifestyle. This combination of nature and nurture also ensures they are as violent as possible. They raid constantly, not only out of violence, but also out of desperation as they have a mutation that keeps them from making a certain chemical in the body. The lack of this chemical is agonizing to them, but a certain, simple food gives them the chemical they lack, and only civilized city centers are capable of producing it.
So here's what I need to know: What type of mineral or chemical deficiency would be agonizing to live with, but not fatal? Preferably something that causes mental issues like hallucinations or extreme aggression. Also, what type of food could possibly give a person the chemical or mineral they are lacking?