It is illegal for a pharmacy to substitute a prescribed medication for anything that is not exactly equivalent. They can and are often required to substitute a generic for a brand name (unless the doctor, insurance or patient directs otherwise), or substitute "dosage form" (capsule for a tablet) But they absolutely can not give a "placebo" in place of an actual medication. In fact pharmacies do not even carry "placebos" on the shelf as a general rule. It IS possible for them accidentally give you the wrong medication however, this is more common than you might think, if you suspect your medication is not what you were supposed to get you should call the pharmacy and ask to speak to the pharmacist. You can also type the description and imprints of any medication into a search engine and gen get a idea of what it is (ie round pink lupin/20.. with the lupin being on side of the pill and the 20 on the other)
Placebo pills can only be prescribed by a doctor first as it works different for everyone. The pill stimulates the menstrual cycle making a woman to go for longer period than usual. Doctors find it best if they are the ones who put you on them, as it makes it easier for them to monitor you.