Pure alprazolam (Xanax) powder was the worst thing I've ever tasted- it's fairly similar to the day-after-zopiclone aftertaste (in my opinion), it lingers for AGES...like, a good 30-40 minutes and absolutely nothing makes it any better. I've gone beyond foods into trying to eat small amounts of salt (which works for bitter things- seriously, sprinkle a bit of salt on your tongue and swirl it round your mouth so it coats your tongue the next time you're drinking poppy tea or something), sugar, citric/tartaric acid, baking soda- nothing makes it at all better.
Admittedly I am a 'supertaster' (I have like 100 times the amount of taste buds as 75% of the population- 1 in 4 people are like that), so most chemicals taste pretty foul- but alprazolam is on another fucking level. Jesus, I can't fucking describe it.
It's like robots have had a party and vomited weird cleaning chemicals in my mouth.