All TB regimens in use were 18 months or longer until the appearance of rifampicin. In 1953, the standard UK regimen was 3SPH/15PH or 3SPH/15SH2. Between 1965 and 1970, EMB replaced PAS. RMP began to be used to treat TB in 1968 and the BTS study in the 1970s showed that 2HRE/7HR was efficacious. In 1984, a BTS study showed that 2HRZ/4HR was efficacious, with a relapse rate of less than 3% after two years. In 1995, with the recognition that INH resistance was increasing, the British Thoracic Society recommended adding EMB or STM to the regimen: 2HREZ/4HR or 2SHRZ/4HR, which are the regimens currently recommended. The WHO also recommend a six-month continuation phase of HR if the patient is still culture positive after 2 months of treatment (approximately 15% of patients with fully sensitive TB) and for those patients who have extensive bilateral cavitation at the start of treatment.