Related Clues:

• Morphine, for one
• Narcotic drug
• Poppy drug
• Smuggled stuff
• Endorphin, basically
• Den drug
• Mind duller
• Smuggler's stock
• Religion, in an oft-quoted metaphor
• Stimulant's opposite
• Addictive stuff
• Painkiller since ancient times
• Poppy yield
• It's a downer
• Drug that's smoked in a pipe