The most expensive substance on Earth. Production of one milligram of positrons costs about $25 million. In theory, we will be able to use antimatter as fuel for spacecrafts in the future. But the drawback today is that to make just one gram of it, all of mankind will have to work for about a year without rest.
Considering that Albert Hoffman the man who synthesized it, not only ingested an amount at least couple of thousand times what is considered a hit by today's standard, and more than once, but he also lived around 60 more years after doing so. Finally passing at 102 years old doesn't sound too screwed up by drugs up to me!