Is it possible to travel from a country where cannabis is legal/decriminalized (such as Germany, Netherlands) to a US state where cannabis is legal/decriminalized (e.g. New York, California) ?
What about when the cannabis is medically prescribed?
Is it possible to travel from a country where cannabis is legal/decriminalized (such as Germany, Netherlands) to a US state where cannabis is legal/decriminalized (e.g. New York, California) ?
What about when the cannabis is medically prescribed?
Absolutely not. As far as US federal law is concerned, there is no such thing as legal cannabis.
As Canada prepares to legalize recreational marijuana starting Oct. 17, 2018, U.S. Customs and Border Protection (CBP) would like to remind travelers that marijuana is a controlled substance under United States federal law. The sale, possession, production, distribution or the facilitation of the aforementioned of both medical and recreational marijuana remains illegal under U.S. federal law. As federal law prohibits the importation and exportation of marijuana, crossing the international border or arriving at a U.S. port of entry with marijuana may result in seizure, fines, and/or arrest, and may impact admissibility.
— CBP Reminds Travelers from Canada that Marijuana Remains Illegal in the United States
Whether it's possible or not is, I suspect, not your real question; the question is whether it's legal. It is not. Here's what the CBP office in Blaine, Washington has to say about it
Release Date Mon, 07/07/2014
BLAINE, Wash. - U.S. Customs and Border Protection (CBP) is reminding travelers crossing the border that possession of any amount of marijuana remains a violation under Federal law.
In enacting the Controlled Substances Act, Congress determined that marijuana is a Schedule I controlled substance and CBP’s enforcement of that Act remains unchanged irrespective of any changes in Washington State law. Whether arriving or exiting the United States, seizure and civil monetary penalties remain in effect for possession of any amount of marijuana.
Foreign visitors who are found to have violated any Federal or State law or regulation relating to a controlled substance risk additional consequences and may be deemed inadmissible to the United States under the Immigration and Nationality Act (INA) and barred from entry.
The United States has been and continues to be a welcoming nation. CBP is charged with securing our Nation’s borders and protecting the homeland while enforcing hundreds of U.S. laws and maintaining the effective flow of travel, trade and tourism at our airports, seaports and land borders.
CBP hopes you enjoy your summer travels, please visit the CBP website for additional information on how to become a “Ready Traveler” and avoid transporting contraband across the border.
U.S. Customs and Border Protection is the unified border agency within the Department of Homeland Security charged with the management, control and protection of our nation's borders at and between the official ports of entry. CBP is charged with keeping terrorists and terrorist weapons out of the country while enforcing hundreds of U.S. laws.
Last Modified: Feb 03, 2021
There is a similar press release from the office in International Falls, Minnesota concerning medically prescribed cannabis; medical use of cannabis is not recognized under US federal law, so the answer in that case is also "no."
Not only is it illegal to IMPORT drugs into the US under US federal law, it is also illegal to EXPORT drugs from the Netherlands under Dutch law.
And KMAR and Customs do inspect luggage (both checked and carry on) of outgoing as well as incoming passengers and WILL arrest you if drugs are found. This btw is not typical to the Netherlands, most any country will do this. And if they suspect but aren't sure you're carrying something illegal, they'll notify authorities in the destination country (and potentially any intermediate stops) to flag you for extra screening on arrival.
Now, under Dutch law a small amount (like a single joint) may only lead to confiscation of the contraband because of the rather lax enforcement of such things, but an extra charge of trying to export drugs may well be added.
As mentioned in other answers you cannot import recreational use cannabis legally to the US, however on the topic of exporting elsewhere,
germany, as it is mentioned in the post body as one possible country to export from.
It is illegal to import and export (non-medical) cannabis to/from Germany under CanG §2 Paragraph 1 Nr. 5:
(1) Es ist verboten,
5. Cannabis einzuführen oder auszuführen,
(unofficial translation:)
(1) It is prohibited,
5. to import or export cannabis,
and you can be charged with up to 3 years in prison or a monetary fine under CanG §34 Paragraph 1 Nr. 5:
(1) Mit Freiheitsstrafe bis zu drei Jahren oder Geldstrafe wird bestraft, wer
5. entgegen § 2 Absatz 1 Nummer 5 Cannabis einführt oder ausführt,
(unofficial translation:)
(1) Anyone who does the following shall be punished with imprisonment for a prison term not exceeding three years or a fine
5. imports or exports cannabis contrary to §2 Paragraph 1 Number 5,
And on the topic of medical cannabis,
As far as I can tell, one may be able to legally import medical cannabis to the US with certain restrictions. Current list of requirements filed to International Narcotics Control Board can be found here, but the basic idea is a need for bringing a valid medical prescription along and for the narcotics to be in the original container. There are additional rules that apply to US residents.
For Germany also, with medical cannabis different rules apply for export and import. For regular exports a license is required under MedCanG §4, but patients can travel with it without such a license, MedCanG §5 Paragraph 3 says:
(1) Einer Erlaubnis nach § 4 bedarf nicht, wer
3. Cannabis zu medizinischen Zwecken auf Grund ärztlicher Verschreibung nach § 3 erworben hat und als Reisebedarf einführt oder ausführt,
(unofficial translation:)
(1) A permit under §4 is not required for anyone who
3. has acquired cannabis for medical purposes on the basis of a medical prescription under §3 and imports or exports it as travel supplies,
For this you may need certain documentation and not all countries allow import of medical cannabis in all forms and quantities with travelers, you will find relevant information (in German) here and the list of requirements for each country filed to INCB on their website here.