Here I will let one of those clickbait articles explain what I am referring to. For they will probably do it better and take less time for me to explain.

http://www.cracked.com/blog/5-brilliant-movie-jokes-that-were-too-obscure-to-get/

Aka Anthony Hopkins / Hannibal is not taking his meds for is pointing out side effects of his meds in a trivia fashion and he wants this "girl" to know that he has beaten the system.

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Now the hissing part of joke was improved by Anthony Hopkins, but it probably was supposed to represent him sucking a pill up to the top of his throat while tipping your head back. That said this previous sentence may not be correct for Hopkins said he took the inspiration from the sound from one of the Dracula movies

But yeah you sometimes use MAO inhibitors (MAOI) with depression, anxiety, and many other disorders. Some of those other disorders including Borderline personality disorder (one of the four disorders of the dramatic / impulsive cluster, the other 3 being antisocial / narcissistic / histrionic) and disorders where people have violent rage / aggression in a reactive manner.

Now Hannibal was not taking his meds, but also it is not clear a MAOI would have helped him for the gene variant (the gene variant discovered in 1990, but the meds were used far prior to this the scientists just knew they work but they did not understand the reason why) for these people seem to have more reactive aggression to stressors instead of a proactive aggression where you do something like you are hunting a person, or you just get your rocks off with messing with a person. Then again these meds may have some effect for they do reduce "voyeuristic" behaviors where some of these people want to show off, including physically exposing their genitals to women.

Oh this gene variant "sometimes nicknamed the Warrior Gene" / or the "super-predator gene" does have some effect on behavior but a very small effect and the media has completely taking the original 1990 finding and followups studies and twisted them and it has probably lead to more prison less attempts at rehabilitation for now we have "science" says the media that some people are just natural predators.

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Sidenote on the MAOI inhibitors, we have 4 main MAOI inhibitors chemical types used for depression (far more than 4 MAO Inhibitors overall), but we now have a version of one of them Selegeline (EMSAM) that you take as a skinpatch like for nicotine and this bypasses the side effects of diet and other things that are caused by the fact you have 90% of the MAO enzyme in your gut, and MAOI inhibitors reduce the amount of this enzyme.