The symptoms of chronic lead poisoning include neurological problems, such as reduced cognitive abilities, or nausea, abdominal pain, irritability, insomnia, metal taste in oral cavity, excess lethargy or hyperactivity, chest pain, headache and, in extreme cases, seizure and coma. There are also associated gastrointestinal problems, such as constipation, diarrhea, vomiting, poor appetite, weight loss, which are common in acute poisoning. Other associated effects are anemia, kidney problems, and reproductive problems.

In humans, lead toxicity sometimes causes the formation of a bluish line along the gums, which is known as the "Burton's line", although this is very uncommon in young children. Blood film examination may reveal "basophilic stippling" of red blood cells, as well as the changes normally associated with iron-deficiency anemia (microcytosis and hypochromia). However, basophillic stippling is also seen in unrelated conditions, such as megaloblastic anemia caused by vitamin B12 (colbalamin) and folate deficiencies.^[13]

Lead affects the peripheral and central nervous system. The most common sign of peripheral neuropathy due to chronic lead poisoning is painless wristdrop (weakness of the extensor muscles of hand) which usually develops after many weeks of exposure.

A direct link between early lead exposure and extreme learning disability has been confirmed by multiple researchers and child advocacy groups.

A May 2000 study by economic consultant Rick Nevin theorizes that lead exposure explains 65% to 90% of the variation in violent crime rates in the U.S.^[14][15]. A July 2007 paper by the same author claims to show a strong association between preschool blood lead and subsequent crime rate trends over several decades across nine different countries^[16]. These results were discussed in a July 2007 Washington Post article, reviving interest in the subject^[17]. Nevin's results reflect peer reviewed findings by Dartmouth Political Scientist Roger D. Masters,^{[18] [19]}and similar work is being done by other researchers. Amherst economist Jessica Reyes' working paper^[20] and Masters' work are both pre-publication and available online.