Tout est poison, rien n'est poison, tout est une question de dose.
Everything is poisonous, nothing is poisonous, it is all a matter of dose.

A barbarous practice, the inconsistency, folly, and injury of which no words can sufficiently describe.
Condemning the use of mercurial medicines.

A drug is a substance which, if injected into a rabbit, produces a paper.

A man who cannot work without his hypodermic needle is a poor doctor. The amount of narcotic you use is inversely proportional to your skill.

According to the estimate of a prominent advertising firm, above 90 per cent, of the earning capacity of the prominent nostrums is represented by their advertising. And all this advertising is based on the well-proven theory of the public's pitiable ignorance and gullibility in the vitally important matter of health.

Despair is better treated with hope, not dope.

Dissections daily convince us of our ignorance of disease, and cause us to blush at our prescriptions. What mischief have we done under the belief of false facts and false theories! We have assisted in multiplying diseases; we have done more; we have increased their mortality. ... I am pursuing Truth, and am indifferent whither I am led, if she is my only leader.

Drugs are not always necessary. Belief in recovery always is.

Hypochondriacs squander large sums of time in search of nostrums by which they vainly hope they may get more time to squander.

If you could see what I almost daily see in my practice … persons … in the very last stages of wretched existence, emaciated to a skeleton, with both tables of the skull almost completely perforated in many places, half the nose gone, with rotten jaws, ulerated throats, breaths most pestiferous more intolerable than poisonous upas, limbs racked with the pains of the Inquisition, minds as imbecile as the puling babe, a grievous burden to themselves and a disgusting spectacle to others, you would exclaim as I have often done, 'O! the lamentable want of science that dictates the abuse (use) of that noxious drug calomel!'
[Calomel is the mercury compound, Hg₂Cl₂.]

Medical men do not know the drugs they use, nor their prices.

One cannot help a man to come to accept his impending death if he remains in severe pain, one cannot give spiritual counsel to a woman who is vomiting, or help a wife and children say their goodbyes to a father who is so drugged that he cannot respond.

Opium is the only drug to' be rely'd on—all the boasted nostrums only take up time, and as the disease [is] often of short duration, or of small quantity, they have gain'd credit which they do not deserve.

Philosophy, like medicine, has plenty of drugs, few good remedies, and hardly any specific cures.

The name of medicine is thought to have been given from 'moderation', modus, that is, from a due proportion, which advises that things be done not to excess, but 'little by little', paulatim. For nature is pained by surfeit but rejoices in moderation. Whence also those who take drugs and antidotes constantly, or to the point of saturation, are sorely vexed, for every immoderation brings not health but danger.

Throw out opium, which the Creator himself seems to prescribe, for we often see the scarlet poppy growing in the cornfields, as if it were foreseen that wherever there is hunger to be fed there must also be a pain to be soothed; throw out a few specifics which our art did not discover, and it is hardly needed to apply; throw out wine, which is a food, and the vapors which produce the miracle of anaesthesia, and I firmly believe that if the whole materia medica [medical drugs], as now used, could be sunk to the bottom of the sea, it would be all the better for mankind,—and all the worse for the fishes.

Tranquilizers to overcome angst, pep pills to wake us up, life pills to ensure blissful sterility. I will lift up my ears unto the pills whence cometh my help.

We can make an exception of opium 'which the creator seems to prescribe, as we often see the scarlet poppy growing in the corn fields' but all other receipts of Omniscience must be condemned. The purple fox-glove, the many-tinted veratrum the lilac stramonium they are all 'noxious' but a little opium it helps the imagination.
Criticizing the medical use of noxious psychoactive drugs.

[Mercurial medicines] affect the human constitution in a peculiar manner, taking, so to speak, an iron grasp of all its systems, and penetrating even to the bones, by which they not only change the healthy action of its vessels, and general structure, but greatly impair and destroy its energies; so that their abuse is rarely overcome. When the tone of the stomach, intestines, or nervous system generally, has been once injured by this mineral ... it could seldom be restored.