It also causes a compulsion to eat.  Like the patient may not even be hungry but the compulsion to eat remains.  You can fight the compulsion to eat and you can fight the extreme hunger such drugs cause but that struggle will eat up all of your emotional reserves and sometimes your physical reserves as well.  Most of the atypical antipsychotics are dire medications that radically alter brain chemistry and should only be used when patients exhibit such extreme symptoms that there is no other way to control them.  It's troublesome that Seroquel has become so commonly used to treat insomnia - it can cause permanent facial and bodily tics, among other problems, and it's prescribed for sleeplessness.