Jennifer Aniston's career-defining performance in hit movie Cake has earned her a flurry of plaudits and award nominations.

The Friends star gives a gritty portrayal of suicidal mom Claire Bennett who is hooked on prescription drugs while struggling to live with debilitating injuries she endured in a car crash that killed her child.

When it was missed from the Oscars shortlist, many critics said it was a miss and should have been included.

But few watching the heart-wrenching Hollywood film will be aware that the screen drama is in fact inspired by a tragic and brutal real life story.

Daily Mail Online has learned that screenwriter Patrick Tobin penned the powerful movie following a devastating family tragedy that saw four of his brother's family slaughtered.

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Acclaim: Critics have hailed Jennifer Aniston's performance in Cake and questioned why it did not at least get her shortlisted for an Oscar

Happiness: Tim and Deb Tobin with their daughter Alyssa. Tim's father-in-law murdered both mother and baby as well as his own wife before killing himself

So much promise: Deb Tobin with Alyssa. Not long after these pictures were taken both were dead

And in an exclusive interview Tobin, 50, opens up about the life-changing event, reveals how it inspired the story behind Cake and explains how his brother Tim gave him his blessing to speak about it for the first time.

'My brother gave me permission to speak about it, and I think it honors his wife and daughter to talk about how they inspired this movie. Because they definitely did,' explains Tobin.

On February 14, 1998, Patrick's brother Tim Tobin made a grisly discovery while picking up his family from his father-in-law's home in the small town of Gillette, Montana – he found four members of his family dead.

His wife Deb's father Don Schell took a .22 calibre pistol and a 357 magnum in the middle of the night and shot dead the three people in the world dearest to him - his wife Rita, his daughter Deb and baby granddaughter Alyssa. Then he killed himself.

The following afternoon Tim found the scene of carnage that will stay with him for as long as he lives.

And seeing his wife Deb and nine-month-old daughter Alyssa lying in a pool of blood still haunts him today.

But what shocked the family most was that Schell, 60, had been a non-violent man all his life and had been a doting grandfather to Tim's young daughter.

Wedding day: Tim Tobin and his groomsmen with his new bride Deb

Family love: Tim Tobin with his wife Deb and baby daughter Alyssa before they were murdered by his father-in-law

The events that took place were drastically out of character and forced Tim to sue GlaxoSmithKline, the British drug giant that makes Paxil, the anti-depressant that Schell had been prescribed to treat a bout of depression.

In 2001 Tobin's family won the case and were awarded $6.4million in compensation.

A U.S. District Court jury decided that taking Paxil was the proximate cause of the deaths of Schell and his wife, daughter and granddaughter.

The jury also found that evidence showed Paxil can cause some people to kill themselves and/or others.

After the slaughter Tim felt he truly had nothing else to live for and he sank into a deep, suicidal depression.

Realizing his brother was in pain, Patrick Tobin packed up his life in Los Angeles and moved back to Montana to be with his sibling and steer him as far away from suicide as possible.

'I moved twelve hundred miles to keep an eye on him - mainly to make sure he didn't kill himself,' says Patrick in an exclusive interview.

'I'd come home and often find Tim in the basement, nursing a bottle of scotch while watching videos of his daughter. Videos of her eating solid food for the first time or crawling.

'When the tapes were done playing I'd help Tim stagger to his bedroom.'

Tobin said his brother replayed the horror of that day over and over in his mind.

'Nothing I could say could take away the horror of Tim discovering the bodies when he went to Deb's father's house to pick up his family,' said Tobin.

'Each night he would take a handful of Tylenol PMs just so he could get an hour or two of dreamless sleep.'

Tobin said he drew on the pain of the tragedy to write the film Cake, which highlights how prescription medication can destroy people's lives.

'A personal inspiration was my brother's experience,' he said. 'The year I spent with him was very hard and it was so painful and horrible to watch.

Writer: Patrick Tobin (right) at the Toronto film festival with, from left director Daniel Barnz, and cast members Sam Worthington, Adriana Barraza, Jennifer Aniston, and Anna Kendrick

'It was never my intention to write about that, but it quickly came out in Jen's character Claire.

'Claire lost her child and her character was tapping into a lot of my brother's pain and our family's pain.

'My brother was self-destructive for a couple of years and didn't care about life and I think he was really looking for a reason to be alive.'

Tobin's powerful movie script caught the attention of some of Hollywood's most celebrated actors including Sam Worthington, Felicity Hoffman, Anna Kendrick and William H. Macy, who star alongside Aniston in the movie.

Yet Tobin said his greatest hope for the movie was that it made people rethink about how we are using medicine to treat pain.

'I could go and see a doctor tomorrow and tell the doctor I'm experiencing extreme pain and I can guarantee you I would get 30 Vicodin pills easily,' says Patrick.

'If I couldn't then I'd go somewhere else instead because there's no system of tracking what I'm taking or who gave it to me.

'Jen's character, Claire, even goes to Tijuana to get hers, and that really happens.

'Cake asks the question, what is pain management? Is it something to make pain go away or is it just dulling it, but keeping it alive at the same time?

'The problem is, in America we say, "We're Americans and we want pain to go away immediately." That's the goal. Make the pain go away.'

But Tobin believes the trick to living with chronic pain is 'coming to terms with it and finding peace with it and learning to deal with it, in spite of it'.

Personal: Tobin was inspired to write a character battling chronic pain - played by Jennifer Aniston - after his brother's tragic experience. She stars alongside Anna Kendrick, whose character commits suicide

He added: 'Advances in pain management are actually narcotics and are addictive and can ruin people's lives.'

Tobin has shocking first-hand experiences of the devastation prescription medication can cause.

But he said the issue is also one that is close to the heart of the movie's leading lady Aniston.

He said: 'Initially I knew nothing about dealing with a lot of pain. I contacted the American Pain Society and talked to doctors.

'There are a wealth of people, especially in Los Angeles, who all they do is manage pain and treat pain.

'One interesting thing I found out was that methadone, the medication they use to treat heroine addiction, is also used in pain medication.

'Jennifer has been very willing to talk about these issues too. Her stuntwoman, Stacy Courtney, is a good friend of Jen's and was in a bad boating accident that saw her become addicted to pain pills.

'Stacy went through a whole ordeal and Jen really relied on Stacy as a source for how to portray the role. They went on the Dr. Oz show together and talked about chronic pain and pain management.

'Jen knows people who have addictions and has worked with people with addictions. For that reason, this was a very tough role for her to play.

'For me, I thought it was an interesting choice not to tell the audience why Jen's character is the way she is until later in the movie. I didn't want people to hate her, so that's where we were able to use humor.'

Tobin says Aniston's character Claire was based on one of his mother's friends, called Wilma.

'She was the only one of my mom's friends who would really speak her mind,' he said.

'She was really honest and blunt and didn't care what anyone thought.'

Pain-filled: Jennifer Aniston's character, Claire, is addicted to prescription pain medication. Tobin says: 'Cake asks the question, what is pain management? Is it something to make pain go away or is it just dulling it, but keeping it alive at the same time?

Patrick is full of praise for the former Friends star – who was so dedicated to the role she stopped exercising for several months and gained weight.

'Jen was so terrific from the beginning,' he said. 'She's so hardworking and she knew it was going to be a tough role because she was playing a person with chronic pain and she had to convey that every second of every scene.

'Jen didn't exercise for several months, and when you're a fit person and you don't exercise, that changes you mentally and that happened for her and she really embraced that.

'When Jen was cast as Claire, it became apparent very quickly she was the perfect choice because she's such a great comedian and it comes so naturally to her.

'The humor in the movie was crucial because it helps to take you along through the story, and Jen managed that perfectly.'

He added: 'The first day I met Jennifer she said, 'Thank you so much for writing such a beautiful script'.

'She was always so lovely to everyone and if we had to work late she would always apologize and thank us all for staying.

'I saw her at the wrap party two weeks later and I barely recognized her. I knew she'd stopped exercising and had put on a little bit of weight for the part, but two weeks after shooting her transformation was incredible, she just looked fantastic.'

The whole experience has been quite surreal for Tobin, who never imagined his family's experience would one day become a box office hit.

'It happened so quickly. As a writer, I wish I'd spent less time worrying and a little more time enjoying it,' he explained.

'It was such an exciting time for me. I kept thinking, 'Oh my God, Jennifer Aniston and Sam Worthington are going to be in this, and Felicity Hoffman and Anna Kendrick and William H. Macy.'

'Friends told me, 'Just enjoy it, this doesn't happen often, just make the most of it.'

'But I felt like I was holding my breath sometimes and should have relaxed more.'

Positive: Despite the tragic background to the story starring Jennifer Aniston, Tobin says: 'The message in this movie is that as bad as life gets there is always, always hope.'

Importantly for Tobin, Cake has been able to honor the devastating family tragedy that almost saw his brother take his own life.

'He and my mom came to the movie premiere in Toronto and were just in tears when they watched it,' Tobin revealed.

'The scene with the wind chimes is actually something that we did for my sister-in-law and my niece. I hadn't told my brother and mom about that. They thought it was so beautiful that they were in the movie.

'Sam Worthington's character, Roy, has also lost his wife and in many ways, Roy is also my brother as well as Claire. I think it is fair to say he inspired both of those characters.

'The year I spent with my brother was the most experience I have had with suicide. Every once in a while, people go through a hard time, but actually being around someone who really doesn't have anything left to live for is just horrible.'

Tobin said his brother Tim, now 46, has since dedicated his life to helping people and he re-trained to become a nurse.

'He stayed strong, he stuck it out and now his life is great,' Tobin said.

'He's remarried, he has two kids now and, as a nurse, he now helps people everyday, which is great.

'A lot of people have empathized with the character of Claire, and so that makes me feel quite strongly that the real message truly is that there is always hope and to just never give up.

'I get a lot of emails now from chronic pain sufferers. I got a lovely letter just yesterday from a woman in Kansas saying thank you for translating my experience and dealing with it in the way you did.