How long does it take for erythema multiforme to clear up?

Erythema multiforme. It depends on the cause, and whether or not the cause is diagnosed and treated. If it's a drug side effect and the drug is stopped, it may start to clear up quickly, in a few days. If it's due to a chronic auto inflammatory condition, it could last a long time, or come and go with flares of the illness.
2-6 weeks. It depends on what caused it in the first place and whether or not it is mild or severe.

Related Questions

My 9 y/o son was diagnosis w/erythema multiforme. He takes xyzal (levocetirizine) to keep the rash minimal but this has lasted 3 mo. Does EM last this long?

Allergy? Erythema multiforme may be from an allergy to medications, or a viral infection which lasts 2-6 weeks if it is mild. If it's worse by now you may want to see your doctor again. Here is a handout on EM: Read more...

How long does rash associated with erythema multiforme last?

1-3 weeks. It is, of course, variable based on each patient. Em is most often self-limited. Mild cases can resolve in 1-2 weeks but more advanced cases can take longer to resolve. Read more...