On a fairly frequent basis last year, technicians at Massachusetts General Hospital injected 40 milligrams of cocaine directly into the bloodstream of cocaine addicts.

With a set of defibrillators kept handy in case of cardiac arrest, the addicts were given MRIs and monitored for changes in heart rate and blood pressure.

The subjects walked out of the hospital with some information on drug addiction, their anonymity and a gift certificate for $260 to a supermarket in exchange for a promise not to use any more cocaine that day.

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