James Franco has reportedly hired a dominatrix to coach him for 'The Adderall Diaries'.

The 36-year-old star is preparing for his role as a drug-addicted writer in his new movie, which is based on the true-crime memoir of the same name by Stephen Elliott, with the help of an S&M expert from New York City.

The actor is said to be especially worried about his raunchy sex scenes with his stunning co-star Amber Heard and wants them to be as realistic as possible.

A source told The Daily Mirror newspaper: '''The Adderall Diaries' is James' baby. His production company picked up the script and he's so excited to be making it.

''The scenes he has been the most nervous about are the S&M scenes, so he's hired an S&M specialist, who also acts as a dominatrix in New York, to coach him.''

Not only does Franco have to deal with nerve-wracking scenes, but he has been conscious of upsetting Heard's fiancé Johnny Depp.

The insider said: ''When Johnny Depp heard about this he immediately demanded to be on set while they were being filmed. He wants Amber to feel in a safe environment and wants to be able to keep a close eye on everything that is happening.

''He is currently shooting his own movie in Boston but comes to New York twice a week to be with Amber on set.''

Christian Slater has just joined the cast as wife-killer murder suspect Hans Reiser, whose case Franco's character becomes increasingly obsessed with.

Pamela Romanowsky will direct and has written the script, while Vince Jolivette is set to produce.