What to do if i took a drug test for employment and didn't tell them the medications i take. and?

You could lose job: When you sign the usual form before giving a pre-employment drug test (or when you are already hired if random or for-cause testing is done), you are stating, often under penalties of perjury, that it is accurate. If you are positive for a potential drug of abuse and didn't tell them about it, they can consider it a positive test and act on it. Talk to the HR person involved and give them info.