Meconic acid, C{7}H{4}O{7}, which is found in opium in combination with the different bases, has also been investigated.

By acting upon meconic acid with ammonia, comenamic acid is formed, and this latter, when heated with zinc dust, yields pyridine.

The same drug contains a peculiar acid called the Meconic; and a vegetable alkali named Narcotine, to which unpleasant stimulating properties are attributed by Majendie.