U.S. regulators are poised to ban the sale of caffeine-containing alcoholic drinks amid rising safety concerns, in a blow to several small but fast-growing drinks companies.

Four Loko, Joose and other fruit-flavored, alcoholic beverages will no longer be able to contain caffeine under a series of regulatory actions expected from the Food and Drug Administration and other agencies this week, according to U.S. Sen. Charles E. Schumer (D., N.Y.) and people familiar with the matter.

Phusion...