I don't think there was ever any implication made that Lupin's or Madam Pomfrey's chocolate was a special "wizard" chocolate - it was therefore likely a regular unenchanted muggle chocolate.
As noted in the comment by gnovice, this question explores the reasons why Muggle chocolate might work: Is there a scientific basis for the healing properties of chocolate?Is there a scientific basis for the healing properties of chocolate?
No mention of chocolate in that context in any of JKR sources.
