AG Barr is to halve the amount of sugar in its leading Irn Bru brand, ahead of a government crackdown on the fizzy drinks industry.
The Cumbernauld-based firm, which also makes Rubicon and Tizer, said it would cut Irn Bru's sugar content from about 10g per 100ml to just below 5g.
It will reduce the calorie count per can from just under 140 to about 66.
AG Barr said the move was part of a "long-standing sugar reduction programme".
It confirmed in a stock market announcement on Wednesday that more than 90% of its portfolio would contain less than 5g of total sugar per 100ml by this autumn.
Tizer is already below that threshold, while the Rubicon carbonates range will all have less than 5g of sugar per 100ml by the middle of this year, the company said.
The UK government plans to introduce a levy on sugary drinks in April 2018.
The Soft Drinks Industry Levy (SDIL) will have two bands in the UK - one for soft drinks with more than 5g of sugar per 100ml and a higher one for drinks with more than 8g per 100ml.
Ministers hope the move will help tackle the nation's obesity problem.
'Blending and balancing'
A spokesman for the company said: "Irn Bru will still be made with sugar. We are not removing all the sugar, but we are reducing the amount.
"Having worked on this for some time, we are carefully blending and balancing a mix of sugar, sweeteners and our original and best flavour essence to deliver the great taste of Irn Bru but with less sugar.
"We're doing this because evidence shows that most consumers want to reduce their sugar intake while still enjoying great tasting drinks.
"86% of consumers are concerned about the amount of sugar in food and drink that they consume.
"That said, we have taken the soft drinks sugar tax thresholds into account when determining the levels of sugar reduction, but never compromising on taste."
In the past year, the company has introduced two new drinks - Irn Bru Xtra and Rubicon Spring - both of which contain no added sugar.
Chief executive Roger White said: "Evidence shows that consumers want to reduce their sugar intake while still enjoying great tasting drinks.
"We've responded by significantly reducing sugar across our portfolio in recent years, through reformulation and innovation.
"Today's announcement builds on this progress and we are now expanding our successful sugar reduction plans to include our iconic Irn Bru brand."
He added: "We will continue to respond to our consumers and adapt to their changing preferences, offering great tasting products that are right for this generation of consumers and the next."