If you know anything at all about U.S. law, you probably know that it comes down hard on any sort of drug use. So what does that mean for a visa applicant who's coming from a country with more permissive laws? Let's take a reasonably likely scenario: You lived in Amsterdam for a while and smoked marijuana there on a few occasions. This wasn't against the law in that country. Could you nevertheless be denied entry into the United States?
It's possible you could be found inadmissible to the U.S. in a situation like this, but not likely.
There are two grounds of inadmissibility to worry about if you've ever used marijuana without being convicted of a crime for doing so.
The doctor who performs your immigration medical exam (required for all immigrant visas, but not usually for nonimmigrant or temporary visas) must determine whether you are inadmissible because you have:
(These grounds of inadmissibility are found in Immigration and Nationality Act Section 212(a)(1)(A)(iii) and (iv).)
There is little risk that occasional marijuana use, standing alone, will be diagnosed as a physical or mental disorder, although if you have exhibited harmful behavior resulting from your use of marijuana, you may be at risk of being found inadmissible.
The drug abuser or addict ground of inadmissibility is not often used to find inadmissibility, because it is difficult to define and prove who is a "drug abuser" or "drug addict."
Frequent marijuana use, even if legal, however, puts you at risk of being found inadmissible as an abuser or addict. Certainly you should be concerned if your legal marijuana use has created some problem that requires you to admit to abuse or addiction in order to participate in a court-ordered program or therapy.
There are places in the world where use of marijuana is not necessarily a crime. If your only use of marijuana was done legally under the laws of a foreign country, you do not have to worry about criminal grounds of inadmissibility.
You still might need to worry if your only use of marijuana was in a U.S. state in which use of marijuana was legal at the time under state law. This is because possession of marijuana for any purpose, including personal use, is a crime under U.S. federal law. Even if the federal government did not convict you of a marijuana offense, immigration law makes you inadmissible if you admit having committed, or admit committing acts that constitute, the federal offense of possessing marijuana.
(This ground of inadmissibility is found in Immigration and Nationality Act Section 212(a)(2)(A)(i)(II).)
How do you "admit" to possessing marijuana, or "admit" doing all the things that would make you guilty of possessing marijuana? It usually requires some kind of formal admission in the course of court proceedings or the immigration application process.
If, for example, you tell the doctor at your visa or adjustment of status medical exam that you've used marijuana, you may have admitted a federal offense. Sometimes a plea or a conviction from a prior criminal case can be an admission of an offense, but the law in this area is complicated. Get an attorney's advice if you think your prior criminal proceedings could contain an admission about marijuana use.
If you admit to possessing less than 30 grams of marijuana, and admit to doing it only once, you can apply for a waiver of inadmissibility under Section 212(h) of the Immigration and Nationality Act in one of two circumstances.
The first is where the incident occurred 15 years before you applied for admission, you are found to be "rehabilitated," and your admission would not be contrary to the national welfare, safety, or security of the United States. The second is where you have a U.S. citizen or lawful permanent resident spouse, fiance, child, or parent who will experience extreme hardship if you are denied admission. Whether you will be granted this waiver is totally up to the U.S. government. Definitely get an attorney's help with this.