Does cold brew have less caffeine?

It depends on the amount of coffee used. With cold brew, you use more ground coffee than with hot brewed coffee. So if you compare one cup of hot brewed black iced vs one cup of espresso made with 1oz ( 30ml) water, the caffeine levels would be about the same, but if comparing two 8oz (235ml) cups of cold brew iced to two shots (1 oz/30 ml each) then the caffeine content would be lower in both cases. The downside is that because espresso has double to triple as much caffeine than a typical cup of coffee does for an identical volume, it also has twice as much acidity and body which may not suite some people's palates.