Even if you ate nothing but foods containing hemp, you wouldn't test positive for drugs. Hemp foods do contain trace amounts of tetrahydrocannabinol (THC), the substance in marijuana that is responsible for the "high" you can get by using the drug. But the minuscule amounts of THC in hemp seeds or the bread, cereals, granola bars, beer and other products made from them will not alter drug tests.
This issue was hotly debated in a recent court case. The manufacturers of hemp foods fought a Drug Enforcement Administration (DEA) rule banning the use of hemp seed or oil containing traces of THC in any foods. In February of 2004, the Ninth Circuit Court of Appeals overturned the DEA rule and held that hemp seeds and oil used in foods couldn't be defined as drugs.
The decision was a victory for consumers because healthy hemp foods may now become more widely available. Many retailers had been reluctant to carry hemp food products as long as the legal case was undecided. Hemp seeds and oil are great sources of omega-3 fatty acids, protein, and fiber. They also provide vitamin E. Look for more hemp foods in the market now that the court case has been resolved.
I recommend eating whole hemp seeds as a good source of omega-3 fatty acids. They're delicious and very easy to prepare. Just pour half a cup of them into a dry skillet placed over medium-high heat and stir them around until they begin to toast and pop. At that point, turn off the heat, stir in a teaspoon of olive oil and then season with salt and pepper or a little soy sauce, red pepper, garlic powder or herbs and eat them as a snack. Prepare only as much as you can eat since the cooked seeds don't keep well.
Andrew Weil, M.D.