Doctors are being told the antibiotic normally used to treat gonorrhoea is no longer effective because the sexually transmitted disease is now largely resistant to it.
The Health Protection Agency says we may be heading to a point when the disease is incurable unless new treatments can be found.
For now, doctors must stop using the usual treatment cefixime and instead use two more powerful antibiotics.
One is a pill and the other a jab.
The HPA say the change is necessary because of increasing resistance.
Tests on samples taken from patients and grown in the laboratory showed reduced susceptibility to the usual antibiotic cefixime in nearly 20% of cases in 2010, compared with just 10% of cases in 2009.