Even inexpensive medications are a waste of money if what you are taking is not effective. Not only is it a waste of money, it could be life threatening and it cost you alot--maybe not in money but in your life expectancy and your health.
With over millions of different medications, interactions with foods, environmental factors, other medications, vitamins, herbal medications, etc; there is a potential risk of losing money, losing effectiveness, potency and having increased effects that cause toxicity and increase harm from not knowing the interactions of the medications that you take.
A few ways to prevent this are:
 Talking with your doctor when a new script is given to you and ask
about potential problems with any supplement or herbal medication that
 Make sure that your doctor has a complete list of all the medications
you take including OTC medications, supplements or herbal remedies so
that before a prescription is written that your doctor can check the new medicine against the list.
 Make a list of all the medications that you are taking and give a copy to your pharmacist, and if you use more than one pharmacy, ensure that all the places you have scripts filled has a copy of it.
Be Pro-active in your own life and make sure that you aren't losing money, aren't going to have major interactions when taking medications, and prevent harm to yourself.