Pooled PREEMPT data ( two studies : a @-week , @-cycle , double-blind , randomised ( @:@ ) , placebo-controlled , parallel-group phase , followed by a @-week , @-cycle , open-label phase ) evaluated onabotulinumtoxinA ( @-@U ) for prophylaxis of headaches in persons with CM ( @days/month with headache @h/day ) .