3M Co. sank the most in six months as adverse exchange-rate moves and high material prices compounded slumping sales in its electronics, health-care and consumer products businesses.

The company cut its 2018 profit forecast to no more than $10 a share, short of even the lowest analyst estimate in a Bloomberg survey. That was the third time this year that the maker of Post-it notes and touch screens has trimmed its outlook.

The diminished outlook underscored the weakness in many of the markets served by 3M, which had already been struggling this year with poor sales of automotive and dental products. Revenue dropped in three of the company’s five main business units during the third quarter.

“Results were weaker than expected, with each segment missing our forecast,’’ John Walsh, an analyst at Credit Suisse Group AG, said in a note to clients. “The reduction to guidance was larger than expected.’’

The shares dropped 6.9 percent to $187.52 at 9:32 p.m. in New York after sliding as much as 7.4 percent for the biggest intraday decline since April 24. 3M slid 14 percent this year through Monday, compared with the 3.9 percent fall of a Standard & Poor’s index of industrial companies.