(Reuters) - Medical device maker Dexcom cut its annual revenue forecast on Thursday, blaming a restructuring of its sales team, fewer customers, and lower revenue from each customer, sending its shares plummeting 40% in extended trading.

The company expects 2024 revenue of about $4 billion to $4.05 billion, compared with its previous forecast of $4.20 billion to $4.35 billion. Analysts on an average were expecting $4.33 billion, according to LSEG data.

Dexcom makes continuous glucose monitors (CGM) - wearable devices that track glucose levels throughout the day without the need for fingerstick blood tests. It has been facing competition from Abbott and Medtronic.

Revenue from Dexcom's US customers dipped quicker than was expected, as customers took advantage of rebates for the new CGM called G7, CEO Kevin Sayer said on a post-earnings call with analysts.

The company also forecast third-quarter revenue of about $975 million to $1 billion, below estimates of $1.15 billion.

It reported second-quarter revenue of $1 billion, compared with estimates of $1.03 billion.

(Reporting by Sneha S K; Editing by Devika Syamnath and Sayantani Ghosh)