Try and find out how much acetaminophen there are in each pill. It's very common and easy to overdose on the tylenol (acetaminophen) in these pills. They usually have about 250 to 375 mg of tylenol in them. Around 3000-4000 mg in a 24 hour period will cause extensive liver damage to the point of liver failure, which kills you in a few days. The number 512 on them may be an indicator of the level of tylenol (512mg of tylenol) which is safe, but make sure you don't take over or even up to 2000 mg of tylenol in a day. The narcotic in percocet is oxycontin, which, in high doses (40-80+ mg) can cause respiratory depression or failure if you don't have a tolerance. Also take care not to mix with other opiates, more tylenol, alcohol or benzodiazepines ie ativan, diazepam, chlorazepam.