parse-pad.js

const urls = `/home/anti-depressants/xanax
/home/heart/lipitor
/home/heart/atorvastatin
/home/heart/aspirin
/drugs/nasal/flonase
/drugs/topical
/drugs/routes/oral/tablets
/drugs/routes/nasal/flonase`;

const parseUrl = (url) => {
  return url.split('/').filter(part => !!part);
};

const parseString = (list) => {
  return list.split(/\n/).map(parseUrl);
};

const reducer = (acc, list) => {
  if (!list.length) return null;

  const key = list.slice(0, 1)[0];
  const rest = list.slice(1);
  const reduced = reducer(acc[key] || {}, rest);

  acc[key] = reduced;

  return acc;
};

const makeJson = (list) => {
  return parseString(list).reduce(reducer, {});
}

const pad = (str, i) => {
  const tab = ' ';
  let padding = '';

  for (let j = 0; j < i * 2; j++) {
    padding += tab;
  }

  return `${padding}- ${str}\n`;
};

const listDrugs = (json, depth = 0) => {
  return Object.keys(json).reduce((str, drug) => {
    const child = json[drug];

    if (child === null) {
      str += pad(drug, depth);
    } else {
      const drugs = listDrugs(child, depth + 1);

      str += (pad(drug, depth) + drugs);
    }

    return str;
  }, '');
};

console.log(
  listDrugs(makeJson(urls))
);