If I were you I'd read the academic literature and then discuss with a GP and/or clinical pharmacist.
You may need to give them a link to research if it's recent. I have found things are inevitably more complicated than they appear at first.
I wouldn't have guessed, for example, that grapefruit variety has such an impact on results - and also when you eat more pith/bioflavanoids (as with whole grapefruit) ... Not as straightforward a question as it seems.
Grapefruit (fruit and/or juice) can adversely interact with quite a number of medications, so it's always wise to read the information label which comes with your meds.
Lots of studies about drug interactions with Grapefruit in various forms and various varieties of Grapefruit - so I suppose it might depend on if you are taking anything else - and how much you need to reduce your cholesterol in the first place.
Try looking on Google Scholar- as I just did. Lots of Grapefruit studies do involve other drugs - or they are looking at weight loss.
The other thing I noticed was that grapefruit seeds are potentally powerful agents!
Can you ask for a 10mg of Atorvastatin if you don't want to take 20mg and see if that reduces your cholesterol just as well as the 20mg?
I’m not sure it’s wise to exchange one for the other. Obviously it’s something to discuss with your GP Surgery, but the NHS website doesn’t advise mixing statins and grapefruit juice. It can increase the amount of Atorvastatin in the bloodstream which could lead to experiencing more side effects.