Everyone metabolises drugs differently. There will always be variations due to genetics, environmental factors (like ingestion of food or drink) and existing health conditions. So no one can make a judgement with full certainty on this, I think.
In the PPH they advise to take 800 mg of propranolol with SN. However, I was perscribed this drug in the past, a dosage of around 20mg. When I was testing out the drug again recently, to see how it would effect me, I nearly fainted after taking only 100 mg.
Nothing is one size fits all, but in my case I've learned I'm very suspectible to medication and I will get dizzy/faint faster than the average person will, likely due to autonomic nervous system dysfunction as a result of CFS.