The Beta Pill was given out during the Die2Nite beta once, the pill was a drug that once taken, gave 30 AP to a single person. Everyone in the town gets one beta pill, and once its gone, there is no way to get it ever again. The beta pill is no longer able to be obtained as it was only given out once in the Die2Nite beta.
The description label states
"For beta-testers only.."