How to display bar names for a horizantal barplot on screen in r shiny?

My bar names are too long so they go off screen. Does anyone know a fix for this? Thanks

 barplot(
                                horiz = TRUE,
                                height = v5,
                                names.arg = trt_name_list,
                                main = "Results",
                                col = "blue",
                                ylab = "Treatment Number",
                                xlab = "Propotion treatment is most favourable",
                                xlim = (range(0, 1)),
                                las = 2
                            )