Novo Nordisk stock collapsed 26% in its worst trading day ever after slashing guidance on Wegovy sales and naming a new CEO.

Investors wiped $70 billion off Novo Nordisk's market value on Tuesday after the maker of weight-loss drug Wegovy issued a profit warning and named a new CEO, as it battles rising competition in the obesity drug market.

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Shares in Danish drugmaker Novo Nordisk were down nearly 20% in pre-market trading Tuesday morning after the company cuts its sales and profit estimates.

A U.S. ban on copycat versions of Novo Nordisk's Wegovy has begun to lift use of the weight loss drug, but the company will need to show more robust growth in the months ahead to bolster market confidence,

The announcement came amid a slump in the company's share price and investor concerns about its experimental drug pipeline and ability to navigate challenges in the US market.