It's been 10 months since the Food & Drug Administration (FDA) first announced a nationwide shortage of Adderall, one of the most widely used medications for attention deficit hyperactivity disorder, & the supply strain could potentially worsen in the months ahead.  While some supply issues have improved, many Americans are still struggling to find & fill prescriptions for the drug & other medications for ADHD that they often rely on to stay focused & complete daily tasks.  Drug-shortage experts said that it's extremely difficult to forecast how much longer the shortages will last because of the lack of transparency in the pharmaceutical industry, & some are concerned about market conditions as children, who are commonly affected by ADHD, head back to school.  “Unfortunately, we might see the shortage worsen. We are heading into back-to-school time, so I am worried about it worsening as we go into that season,” Erin Fox, a pharmacist at the University of Utah & leading expert on US drug shortages, said.  Adderall is one of more than 300 drugs in short supply in the US as of Jun, according to a list from the American Society of Health-System Pharmacists, which represents pharmacists in a variety of health-care settings.  That list also includes Adderall alternatives like methylphenidate, which is commonly known under the brand names Ritalin or Concerta.  Adderall & alternative ADHD medications apart from other drugs are Schedule 2 controlled substances.  That means the federal gov regulates how those drugs are made, prescribed & dispensed because they've been deemed to have a high potential for abuse & could potentially lead to severe psychological or physical dependence.  The designation also means that patients need to get new prescriptions for those drugs every 1-3 months.  Ms of Americans in the US use the drugs to help them concentrate, control their impulses & manage their schoolwork, employment or relationships with others.  ADHD is usually diagnosed in childhood & often lasts into adulthood.  An estimated 6M children have been diagnosed with ADHD & 60% were being treated with medication as of 2016, according to the Centers for Disease Control & Prevention.  Meanwhile, around 8M adults have been diagnosed with the condition, but only about a qtr of that number are getting treatment for it.  Historically, prescriptions for ADHD medications increase as the school semester starts around the US & “there is no indication this year will be different,” according to David Margraf, a pharmaceutical research scientist at the University of Minnesota's Center for Infectious Disease Research & Policy.  Some drugmakers have said they expect to resupply a few ADHD products in Aug or Sep, according to an FDA database on shortages.  But Margraf said “we need to be cautiously optimistic” because drugmakers don’t disclose exact numbers of how much stock they’ll have available by then.