These are sugar pills I’m giving you. Nothing in these pills will have any direct effect on your illness or its symptoms; they have no active ingredient. In biological terms, neither if you eat are you the better; neither if you eat not are you the worse.
However, clinical trials have shown that this illness responds to placebos. A patient’s condition often improves significantly after taking sugar pills — provided that he has been lied to by the doctor and believes that the pills are actual medicine. But “actual medicine” just means something which significantly improves a patient’s condition — so these pills are real medicine, as real as any medicine can be, if and only if the patient believes they are real medicine.
So, what do you believe? Well, if you’re logical, you believe that the pills are effective iff you believe that the pills are effective. They’re the pharmacological equivalent of a Henkin sentence. If you can somehow bootstrap your belief in their effectiveness, that belief will immediately become self-justifying, saving yourself both the cost of prescription medication and the indignity of being deceived by your doctor.
But can you do it?