No—not if you intend to purchase it and use it back home. When you are in your own state, you are required to follow your state’s laws. Because your state doesn’t sanction the use of medicinal marijuana, it is illegal to use it in that state, no matter the purpose, and no matter where you bought it.
In fact, bringing marijuana across state lines could land you in a heap of trouble. Doing so is a serious crime called “trafficking,” which carries harsh fines and jail time. And once you got the marijuana into your state, possessing it there would be another crime (illegal possession), subjecting you to additional fines and jail time. (But if your state has “decriminalized” marijuana, you might incur only a minor punishment—see below for more on decriminalization.)
To learn more about trafficking and illegal marijuana possession, see Marijuana Possession; Laws & Penalties.
In theory, you could travel to one of the 18 states that allow medical marijuana and take advantage of their laws while in that state. But in practice, this will be worky at best and unrealistic for most people. Patients first have to register with the state, and to do so, they must usually be state residents. Residency requirements vary by state (sometimes requiring proof of exclusive residence in the state for a year or more), so you would be unable to take advantage of another state’s medical marijuana laws unless you effectively move to that state.,
The only way your medical marijuana possession and use might be protected is if your state has “decriminalized” marijuana and you’re content to use a very small amount. Decriminalization means that possession of a small quantity of marijuana for personal use (medical or recreational) is an infraction, a minor violation akin to a traffic ticket. Connecticut, Massachusetts, Minnesota, Mississippi, Nebraska, New York, North Carolina, Ohio, and Oregon have decriminalized marijuana without legalizing it for medical use (and several other states have also decriminalized marijuana, but also allow medical use, so they are not listed here).
Typically, violators are subject only to a small fine and first time offenders usually have no criminal record. In states that have decriminalized marijuana, offenders receive citations but they are not arrested unless they possess large amounts or are repeat offenders. Keep in mind that this exception applies only to marijuana possession (and only to small amounts); it does not protect you from being prosecuted for illegally obtaining marijuana, trafficking it into state, or possessing more than the decriminalized amount.
To learn more about decriminalization, see Medical Marijuana: Avoiding Arrest or Conviction.
The bottom line is that when you live in a state that doesn’t allow medicinal marijuana, you cannot legally obtain marijuana—even for medicinal use—from within your own state, or from another state for use at home. Doing either would risk serious criminal charges for illegal possession, trafficking, or both. You may have some limited protection if you live in a state that has decriminalized marijuana, but even then, you must be careful in how you proceed with your possession and use.