The actor who will star alongside Abhay Deol in the political thriller, says that the planned weight gain is giving him sleepless nights.
"I lost quite a bit of weight for `Once Upon A Time in Mumbai` and bulked up a bit for`Dil Toh.` and I have to grow fat for `Shanghai`, so my body has been going through a roller coaster ride," Hashmi told media.
The 31-year-old, who will play a small time criminal, a man living on the margins of society, in the much hyped film, said that the yo-yoing patterns often make him sick.
"It does make me ill and you can only push your body to a limit and I find it very difficult. But when a good role comes your way, you have to put in the effort to make it look credible on screen," said the actor.
With `Shanghai` Hashmi hopes to break a lot of stereotypes that he has accumulated during a seven-year-long career, the most popular being the "serial kisser" tag.
In `Dil Toh` he again played a lothario, who lives off wealthy socialites and is guilt-less about his dalliances.
"He is a typical sicko who thinks he is god`s gift to women and passes himself off as a love guru. But he is confused and feels lost when he finally does fall in love," said the actor about his role.
But Hashmi is unperturbed about the stereotype sticking forever.
"There was a point in my career where I was really upset about the tags that seemed to follow me everywhere but now I am OK with it and know that it can be used to your advantage," said Hashmi.
The actor`s career graph sky rocketed with last year`s hit `Once Upon A Time In Mumbai`, where he played a unscrupulous and ambitious con man and his coming films will break the stereotypes that have dogged him for years, hopes Hashmi.
While the much awaited sequel to `Murder` will delve into the dark world of a serial killer taking his pick in the drug and alcohol fuelled bylanes of Goa, `Dirty Picture`, a bio-pic of the soft porn star Silk Smitha, will see him playing a pimp.
With most of his time spent away from home, the actor says that he misses his 11-month-old son Ayan the most.
While shooting for `Dil Toh`, Hashmi bonded with his co-star Ajay Devgn, who too is a new father, on the subject of fatherhood.
"Children grow up really quick and Ajay advised me to try and spend as much with Ayan as possible. I will be heartbroken if I come back from a month-long shoot and my own son refuses to recognise me and that does happen when they are still babies," said Hashmi.