Valerie Adams, the double Olympic shot‑put champion, cuts an imposing figure as she stretches out her hand to say hello. At 6ft 4in and weighing 260lb (18st 7lb), Adams is even more striking when she settles into an interview which offers some bleak reminders of how doping has tarnished the integrity of athletics.

The Olympic Games begin in Rio de Janeiro next month and the possibility of Adams winning a third successive gold medal, having been cheated temporarily out of victory in London four years ago, will be a gripping subplot. The New Zealander has a powerful personal story – having lost her mother at 15, being one of 18 siblings and winning 56 competitions in a row – but she is at her most compelling when standing up to the cheats and dopers.

Adams offers a blistering response after she is asked an obvious early question. Is Russia’s ban from Rio a significant step forward? “It will definitely be a positive step because if you don’t stop it at the top it will just keep going,” Adams says as she leans forward and talks starkly. “I have no sympathy whatsoever for anyone once they have been done. For me it’s like someone who cheats on their spouse. Once a cheater always a cheater. Kick them out and don’t let them back in. That’s my stance on doping. Zero tolerance. Some people are more lenient towards athletes who do this – but not me. I’m very cut-throat because I have been affected by it three times.

“In 2004, at the Athens Olympics, I finished ninth [behind winner Irina Korzhanenko of Russia, subsequently convicted of doping at those Games] and so I missed out on three extra throws [granted to the top eight competitors]. In 2005 Nadzeya Ostapchuk [of Belarus] got the world championship gold ahead of me but then, eight years later, they retested her results and she got caught for doping. Same thing happened in 2012 at the London Olympics. Me and another shot-putter did a count. We needed two hands to count the 10 shot‑put athletes who have been done for doping in my career.”

Valerie Adams competes at the world indoor championships in Portland in March. Photograph: Ian Walton/Getty Images for IAAF

Is shot put an especially tainted discipline? “It’s across the board. Definitely, in the past, our event was very tainted but now we’ve got a high‑jumper from Russia up for doping.”

Adams shakes her head. Six weeks ago Anna Chicherova, who won gold in the high jump at London 2012, was one of 31 athletes alleged to have failed retaken drug tests from the 2008 Olympics where she was the bronze medallist. Chicherova has been provisionally suspended by the International Association of Athletics Federations despite blaming supplements and vowing to clear her name. “I was surprised by that … a high‑jumper? So it’s potentially spread across the board.

“This whole situation with doping right now is damaging to our sport. It fires me up to educate our young athletes and make them understand it is possible to become a champion without using illegal substances. That’s so important because it ruins your life. You’ve worked so hard for what? You get caught and then what? To win something because of a lie?”

Defending her Olympic title in London, Adams finished second behind Ostapchuk. Seven days later Ostapchuk was stripped of her gold medal after she had tested positive for using the anabolic agent metenolone. It is now shocking to think that, on the London 2012 podium, Adams stood next to Ostapchuk and Evgeniia Kolodko – the Russian bronze medallist who then received a belated silver medal. Last month it was revealed Kolodko had also failed a retrospective test from the London Olympics with B sample results still to be revealed.

“Let’s just say it doesn’t surprise me,” Adams shrugs. Did Adams always suspect Ostapchuk of cheating? “Everybody did. My coach said something straight after we competed in London. They asked him for his thoughts and he said: ‘I have no comment. You will soon understand.’ Seven days later she got done. A few weeks ago Kolodko got done.”

I felt very hurt at first … and then I was happy justice was served. I was one of the lucky ones

Does Adams feel more secure that her sport will be cleaner in Rio? “I really don’t know. The only thing I can control is Valerie. You have to take responsibility for yourself. As long as I do that I am doing the right thing.”

What emotions did Adams experience once Ostapchuk had been caught? “Anger,” she says bluntly. “Then I got upset and everything felt tough.”

There was no happiness in becoming, belatedly, a double Olympic champion? “I felt very hurt at first … and then I was happy justice was served. I was one of the lucky ones. Some only get their medals eight years later. I got my gold medal back in New Zealand after the season was finished at the end of September. They had this venue with 2,500 people inside and hundreds of thousands watching on TV and outside it was packed with people and there were fireworks. It was awesome but it’s still not the special moment you get on the Olympic podium.”

Adams had watched Ostapchuk weep apparently proud tears as she looked at the gold medal dangling from her neck. “Oh, that was such bullshit,” Adams exclaims. “She had practised her acting. She sat up there and cried her crocodile tears. I was smiling but then I was crying, too. I wasn’t crying because I was a sore loser. I was crying because of everything that happened. But I pulled myself together at the medal ceremony and tried to enjoy it for my family. People would die to win a silver medal and here we are – trying to enjoy it but still not happy.”

It is depressing Ostapchuk’s ban will end soon after the Rio Olympics but Adams’s pain, understandably, centres on all she lost in London. “The sweetness of the moment is stolen from you. That was very hard. At least in Beijing I got to savour the moment. London was very bittersweet.”

Valerie Adams won gold at London 2012 but was denied her moment on the podium by Nadzeya Ostapchuk. Photograph: Andrew Fox/The Guardian

Even before Ostapchuk was exposed, Adams faced trauma on the eve of London 2012 because of an administrative error by her federation. “They didn’t confirm I was competing,” Adams sighs. “I found this out less than 24 hours before my event. We were going for my last training session the day before competition and I looked online to see my pool – who else is in my pool and what number thrower am I? I was hitting refresh and I was still not there. I thought: ‘No, no … hit refresh again.’ But no … ‘My name’s not here … where the fuck is my name?”

Adams pulls a face of disbelief. “I ran out of my room and it seemed the management hadn’t signed it off. You enter your team and then you confirm it 48 hours before competition. And she signed the paper without ticking the names. I was fucked up because the Olympic Games are cut-throat but luckily, being the reigning Olympic champion, I was able to get on the list. But I was the very last thrower and they added me into the pool with Ostapchuk. I only got two hours sleep and it was not great.”

Adams is on a carefully managed return after a terrible time plagued by injury. “I got hammered down by injury after I was dominant [and unbeaten] for 56 straight competitions. The last three years I’ve had five surgeries. Two knees, an ankle, one shoulder, one elbow … just a few.” She laughs darkly but then smiles more brightly. “But I’m in pretty good nick after coming back in February in Auckland. My consistency is back but I need one really big throw to pop out … but it’s good to be back on the road into Rio.”

Adams has decided to skip the Anniversary Games in London on 22 July but she hopes to return to the scene of her tangled 2012 Olympic triumph. “Watch this space,” she grins in the hope she will be back for the 2017 world championships in London.

Her past is poignant. In 2000 the 15-year-old Adams stayed with her mother in hospital and then a hospice from the moment her cancer escalated until her death. “I watched the opening ceremony to the Sydney Olympics from Mum’s hospice bed. I was in the hospital and hospice with her, staying there July, August, September. On the night of the Olympics opening ceremony they gave her morphine so she was sleeping. The very next morning, 16 September, she passed away at 9am.

“I kept watching the Olympics all through the next few weeks thinking: ‘Oh my God, I want to be there.’ Four years later I found myself at the Athens Olympics. I owe that to my mum. She supported me until she was too ill. She sacrificed the family finances for me to go training. We didn’t have much money. My family lived on 14 New Zealand dollars a week for five of us. We were very poor but she was my biggest inspiration. When she passed away I was terribly sad but I was relieved too because she was in so much pain.”

How old was her mother when she died? “She was 39. I’m 31 now. The aim of the game now is to break the cycle and live a healthier lifestyle. She was from Tonga and life on the island was different. I grew up being inspired by her and the way in which she helped us survive on such little money. I love my mum dearly but I want to make sure that when my kids come along they have a better life.”

Valerie Adams, fourth right, with 12 of her 17 siblings. Photograph: Twitter/@ValerieAdams84

Her father Sid, an Englishman who settled in New Zealand, had many relationships – and Adams is one of his 18 children. The youngest is Steven Adams, who has just had a fine season in the NBA as a 7ft centre for Oklahoma City Thunder. “I didn’t watch any of his games [in the Western Conference play‑off finals] but I saw his nuts get kicked on a replay. And I heard his monkey comment …”

Adams caused controversy in those play-offs when he described the opposition guards as “quick little monkeys”. What did Valerie make of her brother’s mishap? “I guess there are different cultures but you need to adapt. I know he didn’t mean it. He apologised profusely after it. He’s done exceptionally well but I’ll still knock his two front teeth out. I’m his big sister.”

Adams laughs. She then smiles at the thought that, after all the heartache, 2016 might be a year of joy for her. Her first marriage ended but she has a new husband – her childhood friend Gabriel Price. “I got married three months ago,” Adams says with a grin. “But soon after the wedding I had to go back into camp. I took Gabriel with me and said: ‘Here we are – this is the honeymoon.’ This year has been awesome so far. Most people would just retire with the injuries I had but I didn’t want to finish that way.

“Valerie is still going and I’m going to keep going as long as I can. It’s going to be a tough challenge but anything is possible with a bit of faith. Of course I want the gold in Rio but I would like to help inspire people more – whether it’s changing their lifestyle or working hard or winning clean and living honestly. That’s an even greater goal for me.”