There is, not sure what the amount needed is but chocolate is toxic and will poison you if you eat too much.
I stand corrected.
"Fortunately, the median lethal dose for humans is 1000 milligrams per kilogram of body weight. That means that an 80 kg human would have to eat 5.7 kg of unsweetened dark chocolate for it to kill them (going by a theobromine content of 14 milligrams per gram of dark chocolate, although it varies). For milk chocolate, you’d have to eat around 40 kg."
The real killer in chocolate is Theobromine
"Theobromine is a vasodilator (i.e., it widens blood vessels), a diuretic (makes you urinate) and a heart stimulant. As a result, it can be poisonous."
http://lostinscience.wordpress.com/2012/10/11/death-by-chocolate/
And from
https://www.fishersci.ca/viewmsds.do?catNo=AC258821000
Comes
EMERGENCY OVERVIEW
Warning!
Harmful if swallowed. Target Organs: None known.
Potential Health Effects
Eye: May cause eye irritation.
Skin: May cause skin irritation. May be harmful if absorbed through the skin.
Ingestion: Harmful if swallowed. May cause gastrointestinal irritation with nausea, vomiting and diarrhea.
Inhalation: May cause respiratory tract irritation. May be harmful if inhaled.
Chronic: No information found.