The deal adds a fast-growing brand popular with young women to Celsius’s product line as its own growth slows.

Energy drink maker Celsius Holdings Inc. has entered a definitive agreement to acquire Alani Nutrition LLC for $1.8 billion, including $150 million in tax assets for a net purchase price of $1.65 billion.

The purchase allows Celsius to add a fast-growing beverage popular with young women while better positioning it to compete against rivals Red Bull and Monster.