The rule of law is over.
If this is a federally recognized tribe, they are a sovreign with their own laws.
Do you want them to enforce the following federal drug laws as well?
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Is it Legal to Buy Prescription Drugs from Canada?
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As long as quantities stay low, custom officials usually do not enforce prescription drug laws.
http://thelawdictionary.org/article/is-it-legal-to-buy-prescription-drugs-from-canada/