The new limits affected half of the RTDs sold in New Zealand and required manufacturers to change their containers and the ingredients of their products.
"There were some extensive costs," said Distillers Association head Robert Brewer. "But at the end of the day, it was agreed this was necessary."
There had been some debate among members of the association about the limits, but a consensus was soon reached.
The new code has been adopted by liquor industry giants Bacardi, Diageo, Independent Liquor and others, and the changes will affect popular products such as Woodstock Bourbon and Jim Beam.
Under the new limits, a 440ml can of Woodstock will shrink to 430ml and its alcohol level go from 8 per cent to 6 per cent.
The code also sets limits on how much caffeine can be added to a product, requires labels to clearly display the number of standard drinks in a can, and bans advertising which appeals to minors.
The alcohol limits in the code were more lenient than those originally suggested by the Government.
Alcohol law reforms initially gave the Government power to ban RTDs stronger than 5 per cent or 1.5 standard drinks. Justice Minister Judith Collins later raised this limit to 6 per cent before scrapping the provision in favour of an industry-led code.
She told the Weekend Herald that if it became clear the new measures were not strong enough, the Government would act.
"At this stage, I want to give the voluntary code a chance."
The debate occurred before last month's controversy over alcohol sachets of a single shot of a flavoured alcopop with 20 per cent or more alcohol content. The sachets, branded Cheeky and Sneaky, are the cheapest single drink on sale, at $2.
Police, alcohol action groups and event organisers have labelled the products "disturbing" amid fears they would be used to top up drinks in bars, be smuggled into venues or used to spike drinks.
The voluntary code targeted RTDs because they were believed to be associated with harmful drinking, in particular among young women. The industry disputed this, and research it commissioned showed men over 40 were the biggest consumers of high-strength alcopops.
The research also said that if high-strength alcopops were banned, consumers would move to even stronger, self-mixed drinks.
Industry representatives said the consumption of RTDs, which once claimed about 15 per cent of the alcohol market share, was waning.
Mr Brewer said cider sales were increasing dramatically, in particular among the demographic which consumed RTDs.
"Cider as a category is going gangbusters - it has outstripped any other category in terms of growth."
• Maximum alcohol strength of 7 per cent 2 standard drinks per single serve
• Caffeine level must not be higher than cola products (145mg/litre)
• Number of standard drinks must be clearly displayed on labels
• Products must not target minors in advertising
• Advertising or sponsorship must take place only where 75 per cent of the audience is 18 years or older
• Efforts must be made to minimise harmful consumption