Are you supposed to take an antibiotic after a root canal?

Not always: Unless you have some serious swelling, infection or fever, antibiotics is not necessary or warranted. Ask your dentist.

Root canal: This is up to your dentist. If you have pain and swelling then your dentist might prescribed antibiotics. If you have a dead nerve in the tooth prior to treatment, then you dentist might prescribe antibiotics. It is up to your dentist, but it is not something that is done routinely with every root canal.

Selective Rx: Only if you have swelling or bacterial drainage associated with your tooth, an antibiotic may be prescribed.