My husband has been on 20mg of nadolol since before he started treatment, and continues to be on the same dose now, but initially when they first prescribed 50mg of beta-blocker (before treatment), his heart-rate
and bp took a too-sharp nose dive,
and they quickly cut his dose down, first to 30 then to 20. (The doctor said some people's bodies can be "very sensitive" to beta-blockers, and dosing was often trial-and-error.