"The main difference is the addition of the methyl group that gives methamphetamine its name. The methyl group is like a VIP pass to the brain; it allows the meth to travel faster than amphetamine across the blood-brain barrier and thus makes meth more potent than amphetamines."
The same reasoning applies to why heroine is much stronger that morphine, except this situation involves the addition of an acetyl group.
Feel free to be the first
Please review the linked page for context.
If you can think of something better than this,
please add it to the database