IQ

Previous studies in smaller populations also link in utero exposure of these drugs with neurodevelopmental outcomes in offspring, such as ones linking topiramate and intellectual disability, and those associating valproate and lower IQ.

He alleged the chemical found in toothpaste and regularly used by dentists "is an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease".

Kennedy also asserted that fluoride in the water is “associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease.”

The groups pointed out that the study found low IQ associations only at fluoride concentrations more than double those of the current recommendation of 0.7 milligrams per liter.

He dismissed defence claims about MacPhail's low IQ and learning disabilities, adding the teenager intended to kill Holly and "knew how final death was".