I looked this up in Paul Strathern's "Napoleon in Egypt". On pp. 375-8 Strathern discusses this incident which is alleged to have occured in Jaffa. It is attested by Rene Desgenettes, the Chief Medical Officer of the expedition, that Napoleon ordered opium to be given to his very ill soldiers to avoid them being captured by the Turks and tortured or beheaded. This is in his memoirs and corroborated by one of Bonaparte's secretaries, as well as a note left in the pocketbook of another subordinate. The account left by Sir Sydney Smith also suggests something unusual may have occurred at the Jaffa hospital. The account is also specifically and strenuously denied by other two other French sources on Napoleon's staff, so there is certainly room for debate, although on balance Strathern seems to believe the allegation that opium was given to sick troops.

Regardless of the opium controversy, mortality of the wounded on the retreat from Acre was atrocious, and those with fever or plague were particularly ill cared for. Strathern suggests that a safe conduct could have been requested from the British Admiral, Sir Sydney Smith, at Acre for ships carrying the wounded back to Egypt, and would have likely been granted, but Napoleon did not ask for one.

The wikipedia sentence is a very harsh characterization, in that opium is not primarily a poison and the motivation was not speed but a more merciful end for the afflicted troops.