Can be. After a good meal, eat the tail end off a Naga or Scorpion to find out for sure. Keep a glass of whole milk handy to sip on if you're not used to hot/superhot stuff and need to kill the burn. Chocolate varieties often have an earthy or even slightly metallic taste to some people. Not everybody likes them. I've never personally found the Naga or Scorpion varieties to be bitter, but taste will vary with the individual. Fun fact, chocolate Naga Vipers have very little perceived heat, to me. Other people rate them between upper level Fatalii and Bhut range on average, but I've never eaten one that felt as hot as even a habanero. Whatever capsaicinoids are in those, I am apparently not very sensitive to them.