He hardly drank when he became an All Black in 1956, but that all changed for the worst during the All Blacks tour of South Africa in 1960.
MacEwan was forced to take a break from the tour due to exhaustion after the ABs' win in the second test in Cape Town, with a local doctor telling him: "You need to relax more, you need to be imbibing more from the top shelf".
It was advice he heeded to the detriment of his health, eventually returning to the tour as a heavy drinker. And worst of all, he hid his new addiction from his teammates.
Booze – and how it made him behave - ended his test career after he gave the All Blacks selectors a verbal barrage at a function in 1962.
His alcoholism continued after his playing days; peaking as his work life spun out of control, including being charged by police for theft and then making an attempt on his life.
Back then there was little support for players – or ex-players - doing it tough.
And MacEwan is definitely not alone in terms of players from his era who have battled severe alcohol issues either during and after their careers.
Like MacEwan, 1964-66 All Black midfielder Ron Rangi didn't drink in the early stages of his career. But as his All Blacks career took off, so too did his battle with the alcohol.
His career came to a staggering halt after being caught trying to souvenir a bottle of whiskey from an aftermatch function. Instead of being offered help, he was effectively banned from playing for the All Blacks.
Nowadays, sanctions would be handed down to any misbehaving. But help, thankfully, would also be provided.
New Zealand Rugby has certainly stepped up over the past decade when it comes to rugby's relationship with alcohol.
Recent All Blacks who have got themselves in trouble while drinking – including Jimmy Cowan and Zac Guildford – were both aided by the national body; as well as sanctioned for their respective off-field incidents.
And culture-wise, the release of its Respect and Responsibility Review in late 2017 saw New Zealand Rugby boss Steve Tew call on all clubs to take an approach to alcohol that reflected "responsible hosting"; including food, a range of non-alcoholic options and not to overdo celebrations.
The New Zealand Rugby Players' Association also plays a leading role in protecting the well-being of professional players in New Zealand – being proactive when it comes to tackling issues which could face its members.
Services it offers are proactive workshops on looking after mental health, and advice on issues such as financial planning, personal support, behaviour risk, and job hunting help.
A message to members on its website states: "Remember – a problem shared is a problem halved."
The Players' Association also operates a Benevolent and Welfare Fund for players whose careers are cut short or who "are suffering hardship".
MacEwan's story is both harrowing and inspiring. He is coming up 40 years booze-free, has worked as a prison chaplain and now regards helping others with their addictions as being more rewarding than the 52 times he proudly pulled on the All Blacks jersey.
