Some quotes from the Vedabase about chocolate:
Cocoa and chocolate are not to be taken as they are intoxicants.
>>> Ref. VedaBase => Letter to: Surasrestha — Los Angeles 14 June, 1972
If chocolate is not an intoxicant, it can be offered to the Deities.
>>> Ref. VedaBase => From: Paramahamsa – SL_750608_A1
Tea contains caffeine, while chocolate and cocoa contain the stimulant theobromine as well.
And you refused to grant dispensations about what we could eat: “Krishna doesn’t take any [chocolate], so we cannot offer it.”
Flesh, condiments, eggs, tea, coffee, chocolate, and all other stimulants have a powerful influence directly upon the blood; and through nervous sympathy with the brain, the passions are aroused.
Aside from Vedic standards, even by the standard of Swamiji’s New York disciples the devotees in San Francisco were not very strict. Some continued going to the doughnut shop, eating food without offering it to Krsna, and eating forbidden things like chocolate and commercial ice cream.
>>> Ref. VedaBase => SPL 22: “Swami Invites the Hippies”
I was aware of the thing and that it was a pretty heavy one, much more austerities than other groups-like no coffee, chocolate, or tea.
>>> Ref. VedaBase => SPL 29: Unlimited Opportunity, Limited Time
Bhavananda, once a film-maker with Andy Warhol, gave up the “synthetic world” of materialism for a spiritual life of reading the Bhagavad-gita, Bible of the Krsna followers, and abstaining from tobacco, liquor, drugs and even chocolate.
>>> Ref. VedaBase => July, 1970
“How are you going to cook? Anyone want Kellogg’s Corn Flakes or ice cream?
How about chocolate?”
“No, no. You can’t offer these things to Krsna,” Visnujana explains. “We buy everything fresh, prepare it with love, and offer it with devotion to Krsna.”
>>> Ref. VedaBase => Kripamayi devi dasi:
not taking intoxicants, means eschewing even the milder anodynes such as tea and chocolate.
>>> Ref. VedaBase => Dealing with spiritual failure
ISKCON Law Book (1997) 8.5.1: Prohibition of Chocolate As it contains
various stimulants like caffeine (contained in coffee), theine (contained in black tea) and theobromine (contained in cocoa), chocolate should not be eaten by ISKCON devotees.