I'm currently taking the antibiotic ________ , and I want to take MDMA -- is this safe?
If you are sick enough to be taking an antibiotic, there is a good chance that you aren't healthy enough to take MDMA. MDMA supresses the immunes system, making it easier to catch viruses and infections. Thus, if you are trying to fight an infection, and you take MDMA, there is a good chance that it will take you longer to recover from your infection. For this reason, it is strongly recommended that you wait until you are in better health before taking MDMA.
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Most antibiotics are theoretically safe to combine with MDMA. I say 'theoretically' because although there are no forseeable interactions, there has been no medical research on the combination of MDMA and antibiotics.
There are a number of people who have rolled safely on antibiotics, and to date a bad interaction between an antibiotic and MDMA has never been reported. However, this does not gaurantee that you won't have an interaction, so keep this in mind.