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Two other measures now under consideration could reduce the harmful effects still further. British research, cited repeatedly at Nelson's hearings, suggests that the risk of clotting is somewhat greater with the sequential pills. It is also directly related to the amount of estrogen in either type of Pill, and is markedly increased if the estrogen component is more than 50 micrograms (less than two millionths of an ounce). Britain has already officially discouraged the dispensing of pills with any higher estrogen content. By this reasoning, women in the U.S. would find themselves limited to seven out of the 20 oral contraceptives now on the market. The "one-every-day" Pill containing no estrogen should virtually eliminate clotting risks, though it will still require intensive study of other side effects. As, in fact, do all potent drugs.
-Two types are approved for general prescription: 1) 21 daily combination pills containing synthetic equivalents of the hormones progesterone and estrogen, with the latter in a microscopic dose; 2) sequential pills, which provide tablets of an estrogen alone for 14 to 16 days, followed by five to seven combination tablets. A third variety, the "one-everyday" pill of progestin (progesterone equivalent) only, is being tested but is not yet licensed for U.S. prescription.