Though the general impression is otherwise, the users of heroin acquire the habit as quickly and as easily as if they took morphine. Many cough and asthma preparations contain heroin, simply for temporary alleviation, since, like opium, it has no curative power whatever. From time to time I have had to treat cases of heroin-taking in which the victims had thought to satisfy their need for an opiate without forming a habit. In the cases where it was given by prescription, it was so given by the physician in the sincere belief that it would not create a habit. All this despite the fact that heroin is three times stronger than morphine, and despite the fact that physicians know that anything which will do the work of an opiate is an opiate. Codeine, notwithstanding the fact that it is weaker than morphine, is likewise habit-forming; yet doctors prescribe it on account of its relative mildness, even though they know that it is the cumulative effect of continued doses, and not the quantity of morphine in the dose, which results in habit. As with morphine, to use either of these drugs effectively means in the long run the necessary increase of the dose up to the limit of physical tolerance.
The most harmful of all habit-forming drugs is cocaine. Nothing so quickly undermines its victim or provides so short a cut to the insane asylum. It differs from opium in two important ways. A man does not acquire a habit from cocaine in the sense that it is virtually impossible for him to leave it off without medical treatment. He can do so, although he rarely does. On withdrawal, he experiences only an intense and horrible depression, together with a physical languor which results in a sleepiness that cannot be shaken off. Opium withdrawal, on the other hand, results in sleeplessness and extreme nervous and physical disorder. In action, too, cocaine is exactly the opposite of opium, for cocaine is an extreme stimulant. Its stimulus wears off quickly and leaves a corresponding depression, but it confers half an hour of capability of intense effort. That is why bicycle-riders, prize-fighters, and race-horses are often doctored, or "doped," with cocaine. When cocaine gives out, its victim invariably resorts to alcohol for stimulus; alcoholics, however, when deprived of alcohol, generally drift into the use of morphine.