Breaking Bad
The One Who Knocks, The Danger, Walter White. AMC

Breaking Bad star Bryan Cranston has revealed what was used as a substitute for the killer drug for the hit AMC TV show.

"We use cotton candy flavoured rock candy," Cranston told Australia's Kiis FM, while on the promotional tour for new film Godzilla.

"It's vile tasting pieces of sugar."

The 58-year-old actor also revealed that the cast and crew would eat the meth substitute for energy during the show's longer, more laborious shoots: "In the 16th, 17th hours, some days of working on the show, I first noticed Aaron Paul taking a handful of products that we were making and he's eating it and he's like 'I just need some sugar, I'm crashing'."

Bryan Cranston in Gareth Edwards' Godzilla Legendary Pictures

"I tried it and then pretty soon the entire crew was eating the sugar because we're all exhausted and we wanted the sugar rush to get us through the night."

Considered among the greatest ever television series, Breaking Bad came to a dramatic, epic end last, year after five years.

Cranston also told the station about being taught how to cook meth during his preparation for the show. "They taught Aaron Paul and I the steps on how to make crystal meth at that level of purity.

"They didn't want us to write anything down but it was so detailed that an hour later, I'd already forgot about the orders of things and I forgot the name of things. You really have to be a student of chemistry to be able to do it really well like Walter White made it."

Bryan Cranston can currently be seen in Godzilla, which is in cinemas now.