Juicer machine called nutribullet has warning label to contact your doctor before using if taking cholesterol-lowering meds which I am. Any concerns?

Not concerned. I am not sure what they are getting at except to protect themselves from litigation. The one significant interaction between statins ( atorva-, simva-, and lova-) is with grapefruit so one should avoid this combination in excess. As with anything in life moderation is the key.
Can affect statins. Grape fruit can affect metabolism of statins and can interfere with other meds. Just consult your doctor. Go thru the list of meds your on to make sure theres no problem. Sometimes its a matter of separating the juice and the medication so they are not taken together. .
Citrus and Drugs. It depends what you blend in the machine. Grapefruit and limes, in particular can interfere with some blood pressure drugs and zocor and lipitor, (atorvastatin) for example. Check with your doctor to determine what drug interactions might be harmful and he can help you choose what juices to blend in your machine that won't cause potential harmful interactions.