The actress - who plays addict Rainie Cross - insisted that if the plot saved one life, it had been worth doing.
More than 200 complaints were received about scenes showing Phil Mitchell (Steve McFadden) and Rainie using the drugs last week. Natalie Cassidy also blasted the scenes, calling them "outrageous".
"I wasn't surprised that people complained because it's pushed a boundary," Franks told The Sun. "But in my opinion, the good that comes from storylines like this far outweighs whatever concerns people might have."
She continued: "It's been very well handled and as true and real as it could be before the watershed. They've been very brave with it and I give full credit to EastEnders for that."
Franks added that the plot, which is based on a real person's story, will have helped some viewers.
"For all the complaints there will be a lot of people who've been helped and seen the helpline information," she said. "If EastEnders has saved one life by putting this story out it's been worth it. We shouldn't shy away from it.
"The whole point of soaps is to reflect a certain amount of everyday life. Some of it is going to be light entertainment, some isn't."
She also hit out at the criticism that Phil's addiction was too instant, and told how bosses at the BBC soap had put her in touch with the DrugScope charity so that she fully understood her character.
She told the paper: "From my understanding and the research I did, this drug grips you from the first hit. It is not the type of drug you can just try once. You can take it once and be addicted for a long time."
> BBC defends 'EastEnders' drug scenes