These days, the medicine cabinet is truly a family affair. More than a quarter of U.S. kids and teens are taking a medication on a [longterm] basis. Nearly 7% are on two or more such drugs. Doctors and parents warn that prescribing medications to children can be problematic. There is limited research available about many drugs' effects in kids. And health-care providers and families need to be vigilant to assess the medicines' impact, both intended and not. Although the effects of some medications, like cholesterol-lowering statins, have been extensively researched in adults, the consequences of using such drugs for the bulk of a patient's lifespan are little understood. Many medications kids take on a regular basis are well known, including treatments for asthma and attention-deficit hyperactivity disorder. But children and teens are also taking a wide variety of other medications once considered only to be for adults, from statins to diabetes pills and sleep drugs, according to figures provided to The Wall Street Journal by IMS Health, a research firm. Prescriptions for antihypertensives in people age 19 and younger could hit 5.5 million this year.