The answer to this question is not an easy one. Nurses are responsible for setting up the medications properly and educating the patient on the need to take each medication. Also, the nurse must inform the patient on the times that each medication is due. Involvement of the patient in setting up the medications is ideal. However, once the pill box has been set up and patient has been educated, patients may choose not to follow the nurse's instructions. Nurses must provide proof of proper education and the patient's response to that education. Ideally, the nurse and the patient should be jointly responsible for making sure the medications are taken properly.
It is the responsibility of the nurse to make sure that the patient understands what medications she/he has set up for the patient and that they know when and how to take them. Then the nurse needs to follow her company's policy in documenting that education to the patient to prove that the education was in place. After that it is the patients responsibility to actually take the medications as they are set up and the nurse has explained them to them.
If the nurse suspects that the patient has been taking the pills incorrectly whether intentionally or unintentionally the nurse needs to document exactly why she believes this (pills left over, pills used up too quickly, obvious side effects in the patient, etc.). Document facts and observations not just hunches or "feelings" support your belief with facts. Then following their companies policy they need to report this misuse to their supervisor/physician. The care plan for this type of patient may need to be changed following your supervisor's notification.
The division of responsibility for taking medicines properly must be shared by the patient and the nurse. The responsibility of the nurse will depend very much on the condition of the patient. If the patient is completely bed ridden and is sleeping most of the time under the effect of medication, the nurse may be almost fully responsible for proper medication. In some cases the medication may have to be administered through injection or intravenous drip. In such cases patient has no role to play except let the nurse do their job.
However if the patient is just down with some mild infection and is advised rest at home, there is very little role for the nurse to play.
One final word of caution, whoever may be theoretically responsible for proper medication, it is always the patient who suffers most by improper medication. Therefore it is in the interest of the patient that the patient and his near and dear ones also are careful about the medication.