Novartis has warned that its profit may decline this year as it ramps up marketing spending on new heart failure drug Entresto after a disappointing start for the medicine.
Combined with falling sales of leukaemia treatment Gleevec, core operating income will be "broadly in line with the prior year or decline low-single digit" at constant currencies, it said.
The company had previously said profit would be roughly the same.
The world's biggest prescription drugmaker, which reported slightly better than expected second-quarter profit, is banking on new drugs such as Entresto and Cosentyx for psoriasis to offset generic competition to Gleevec.
Entresto is seen as potentially a huge product, with annual sales of $5 billion or more, but has struggled to gain traction in the all-important US market since its launch last summer, although it is doing better in Europe.
Entresto sales in the second quarter were $32m, while Cosentyx brought in $260m.
The Swiss company reiterated its forecast that Entresto would generate around $200m in sales in the whole of 2016.
Prospects for Entresto were boosted in May when new medical guidelines on the treatment of heart failure strongly endorsed it.
The company's chief executive Joe Jimenez said that Novartis needed to capitalise on this by spending more to market the drug in the second half.
Industry analysts said the decision to ramp up spending on sales representatives made sense, even with the downgrade to 2016 profit, but it suggested past planning shortfalls.
Novartis is also struggling with a weak performance by its Alcon eyecare business, although analysts said there were signs of sales turnaround here.
Second-quarter core net income, which excludes some items, fell to $2.93 billion, compared with the $2.83 billion average of forecasts from analysts polled by Reuters.
Core operating income fell 4% at constant currencies to $3.33 billion, also ahead of market expectations.
Sales came in at $12.47 billion, down a reported 2% and flat at constant currencies compared with the poll average of $12.19 billion.
