Can pep effect a syphilis test and how long after unprotected sex should i test for syphilis?

Doxycycline PEP can have an effect on a syphilis test. I recommend testing for syphilis 3 weeks and 3 months after exposure. You can validate this advice by calling your local public health department.

Yes, PEP given within 24 hours of exposure may prevent the infection up to 75% then the syphilis test (RPR/VDRL) should be negative, i.e. PEP affects the test result because PEP is effective. With or without PEP, you can have the test done after 6 weeks. If screening test is positive and confirmed with FTA/ABS or TPPA, then you need treatment with Penicillin or Doxycycline (for PCN allergy).