I was prescribed medications that when combined can cause internal bleeding. Do I have a malpractice case even if I didn't take them?

If a health care provider is negligent, you may be able to hold that provider responsible for their negligence and for the damages that are suffered. However, that means that there actually has to be damages. In your case, since you were lucky and you didn't actually take the drugs or suffer any harm, your damages would either be very small or non-existent. This means it is generally not going to be worth it to sue. 

Medical malpractice is a special body of tort law designed to provide compensation to those who are hurt by their doctors or healthcare providers. There are two things you need to prove in a malpractice case: that negligence (a breach of the standard of care) occurred, and that the negligence was a direct cause of some kind of harm. 

The reason that both of these elements are required is because:

• Doctors/health care providers can't possibly be liable for every single thing that goes wrong. If they are careful and provide reasonably competent care, they are thus absolved of liability for problems that occur.
• Civil lawsuits are designed to make a plaintiff whole and ensure he doesn't suffer financial loss as a result of negligence. These losses must be some kind of actual measurable loss, like injury that causes you to incur medical bills or miss work, and/or injury that causes you pain and suffering or emotional distress. If you aren't injured, then you are already "whole" and haven't been a victim of the negligence.

Thus, while you may be able to sue, you'd probably be awarded only nominal damages, which is a very, very small award (usually around $1 or $2) which indicates that you did have a legal cause of action but that you didn't suffer because of it. This generally means it is not worth it to sue.

If you are concerned about the pharmacy's carelessness, you should consider speaking with a lawyer. Your attorney can help you to determine if a lawsuit is worth it, or may be able to help you notify a state licensing board in your state about what went on so the proper steps can be taken to make sure the pharmacist is more careful in the future.