Are they forgetful? Have had some really good outcomes with using the Phillips medication tower, which dispenses meds on a timer and has a voice reminder alarm when they are dispensed. That unit also has the option of calling a caregiver if the person does not dispense them (but obviously you need a willing person to monitor that...). This also works pretty well if you are worried about abuse of bentos or pain meds or something, because the machine can be locked. I think only Medicaid reimburses for med-set up so that's a potential limitation...but it does cover the cost of the tower which is pretty cool.
Much harder situation if they are throwing them out or not taking because of side effects or what not...in that case you would really want to work on developing a rapport and encourage the patient to be honest and then make sure the provider is aware of side effects so they can change the dosage or try something else. Sometimes side effects can be managed by switching meds, adding another med (I.e. Abilify manages lactation side effect of Risperdal), or just changing the dose or schedule.