First off you should keep a list of all your medication with you all the time. Make sure you have both the brand name and the generic name and as well as the doses. I also recommend that you keep a copy on your fridge. Paramedics will look there first.
One of the main causes of medication errors is poor communication and misunderstanding. If you are not sure of what your doctor is saying ask him to write it down for you. One assumption is that your doctor knows what medications you're taking. Don't bet on it. Your doctor may have your medication list from a visit six months ago. He does have changes that your other providers have made. So when your cardiologist makes a change in your dosage it does not magically update your primary doctors list. Computers make it easier to track things like medication but they are not always correct. Remember the adage "garbage in; garbage out" If an error was made in data entry it will translate into repeated mistakes. One mistake I've seen is patients overdosing on medication because they are taking pills from the generically labled bottle and the same pills from the brand labled bottle thinking they are different. Example: I had a patient taking one lasix and one furosemide not realizing they are the same. Pharmacies can make errors also. Check the medication on the label to make sure it is correct. I have seen Quinidine sulfate (used heart arrythmia) dispensed instead of Quinine sulfate (used for leg cramps). Handwritting is an issue but accidentially clicking the wrong drug on computer is possible also. If you receive desoxin (amphetamine) instead of digoxin (cardiac drug to slow the heart) you're in big trouble.
So here is my list of recommendations:
1) Keep an up-to-date record of your medications with you and on the fridge if you live alone.
2)Let your doctors know of medication changes at the time of the visit
3)Have you doctor write down instructions if you are not sure.
4)Ask if a new medication is an addition to your regimen or a substution.
5)Do not stockpile medications. You will end up with multiple bottles of unknown medications.
6)Do not mix tablets in bottles
7)Check you medication label when you pick it up from the pharmacy.
8)Bring all your medications with you when you go to the doctor.