Syphilis can generally be completely cured nowadays, except neurosyphilis which is somewhat harder to treat, as ordinary syphilis is curable and neurosyphilis may relapse occasionally. However, most current cases of syphilis fall into categories of latent, primary, or secondary syphilis. Tertiary syphilis is less common, and forms such as neurosyphilis and osteal syphilis belong to this stage. Therefore, when treated at a regular hospital with a standard treatment regimen, primarily using penicillin, administered as a long-acting intramuscular injection once a week, the recommended course of treatment usually consists of three to four weeks. If there is an allergy to penicillin, doxycycline can be used as an oral substitute for half a month.