They cause suffering in body and soul. Many patients have the terrible feeling that their body does not belong to them anymore. Limbs and face can be subject to involuntary movements. This side effect is called Tardive Dyskinesia. But these drugs have been in use for only a few years.
Nobody can predict their long-term effect.
The effects on the soul can also be terrible. Neuroleptics can make you unable to feel happiness about anything. They can help when a person has lost his sense of reality, when communication with him has become impossible. And neuroleptics are not too dangerous if taken for, say, three months. But most psychiatrists insist that neuroleptic drugs should be taken for a lifetime.