Taking a common arthritis drug along with the morning-after pill Plan B could boost the contraceptive’s effectiveness. That's according to new research published Wednesday in the Lancet. Scientists estimate that is Plan B is about 95% effective at preventing pregnancy when taken within a day after unprotected sex. It drops to 58% when taken within three days. The new study suggests the drug’s efficacy could be maintained at about 95% within three days of unprotected sex if the contraceptive is taken with piroxicam. That's an anti-inflammatory painkiller typically prescribed for arthritis.