Why was King George 3rd mad?

It is now generally assumed by scientists that he was not "mad" as in 'mentally imbalanced', but that he suffered from porphyria, a genetic defect causing faulty synthesis of protein and dysfunction of the central nervous system. The reason that George's bouts of porphyria lasted as long as they did was probably the fact that the medicin he was given contained arsenic, which worsened his illness instead of curing it.