In the United States, the public's perception of hemp as marijuana has blocked hemp from becoming a useful crop and product," in spite of its vital importance prior to World War II. Ideally, according to Britain's Department for Environment, Food and Rural Affairs, the herb should be desiccated and harvested towards the end of flowering. This early cropping reduces the seed yield but improves the fiber yield and quality. In these strains of industrial hemp* the tetrahydrocannabinol (THC) content would have been very low.
It is sometimes supposed that an excerpt from Washington's diary, which reads "Began to seperate [sic] the Male from the Female hemp at Do.&—rather too late" is evidence that he was trying to grow female plants for the THC found in the flowers. However, the editorial remark accompanying the diary states that "This may arise from their [the male] being coarser, and the stalks larger" In subsequent days, he describes soaking the hemp (to make the fibers usable) and harvesting the seeds, suggesting that he was growing hemp for industrial purposes, not recreational.
Air-dried stem yields in Ontario have from 1998 and onward ranged from 2.6–14.0 tonnes of dry, retted stalks per hectare (1–5.5 t/ac) at 12% moisture. Yields in Kent County, have averaged 8.75 t/ha (3.5 t/ac). Northern Ontario crops averaged 6.1 t/ha (2.5 t/ac) in 1998. Statistic for the European Union for 2008 to 2010 say that the average yield of hemp straw has varied between 6.3 and 7.3 ton per ha. Only a part of that is bast fiber. Around one tonne of bast fiber and 2–3 tonnes of core material can be decorticated from 3–4 tonnes of good-quality, dry-retted straw. For an annual yield of this level is it in Ontario recommended to add nitrogen (N):70–110 kg/ha, phosphate (P2O5): up to 80 kg/ha and potash (K2O): 40–90 kg/ha. The average yield of dry hemp stalks in Europe was 6 ton/ha (2.4 ton/ac) in 2001 and 2002.
Hemp is possibly one of the earliest plants to be cultivated. An archeological site in the Oki Islands near Japan contained cannabis achenes from about 8000 BC, probably signifying use of the plant. Hemp use archaeologically dates back to the Neolithic Age in China, with hemp fiber imprints found on Yangshao culture pottery dating from the 5th millennium BC. The Chinese later used hemp to make clothes, shoes, ropes, and an early form of paper. The classical Greek historian Herodotus (ca. 480 BC) reported that the inhabitants of Scythia would often inhale the vapors of hemp-seed smoke, both as ritual and for their own pleasurable recreation.
Since hemp seed is very low in sodium and calories and is a complete protein, it can be eaten in large quantities without fear of gaining too much weight. Complete proteins make the body feel full because all of the necessary amino acids have been taken in through food, thereby inhibiting the release of ghrelin and curbing hunger pains. This reduces the chances of overeating and subsequent weight gain. Also, fiber makes the body feel full and stimulates good digestion and fast passage of bowels, which can reduce weight and increase the efficient absorption of nutrients.
As of 2011, hemp seeds are not known to cause any interactions with common medications, but you should talk to your doctor or naturopath about any over-the-counter or prescription drugs you are taking before adding hemp seeds to your diet. Blue Shield of California recommends caution to anyone taking anticoagulant drugs, since hemp seeds inhibit platelets and may pose a bleeding risk.