A single marijuana cigarette has the same effect on the lungs as smoking up to five cigarettes in succession.
A to Z Health Guide 2007
The scientific bulletin of the year may be the stem-cell breakthrough. But 2007 provided a whole alphabet of big medical news. TIME's A-to-Z guide reviews them
—By Coco Masters, Alice Park, Carolyn Sayre, Tiffany Sharples, Alexandra Silver and Kate Stinchfield
Marijuana