Very few things in the universe are 100 percent good or 100 percent bad. Cannabis is perfectly ordinary in having a mixture of good qualities (medical benefits) and bad qualities (medical risks). The people who want to make money – lots of money, by the way – from selling marijuana do a perfectly fine job of pointing out the good. But they don’t educate the public about the possible risks. They know it will be bad for business. Astonishingly, there are no laws that require them to talk about risks  —  so they don’t. And that is 100 percent bad.

But the medical value of cannabis is actually a very old story. The only thing new is the part about it being safe.

Cannabis was widely used in Medicine from the mid-1800s through the early 20th century. Before it became a political hot potato or a reservoir for moral angst, cannabis was just an ordinary medicine. It was nothing more than another tool in the box for the turn-of-the-last-century physician.

Pharmacology textbooks of the era covered cannabis as matter-of-factly as they did everything else. They described what it looks like, what it smells like, how to prepare and store it, and what it’s useful for. One text specifies that physicians should keep 4 ounces of Cannabis Indica in stock at all times – and should also carry some in their house call bag. The books also, of course, described the side effects.

Readers of these century-old textbooks will find that most of today’s medical applications of marijuana were known as far back as the 1880s. Among other indications (like gonorrhea), cannabis was recommended to treat: pain, insomnia, anxiety, muscle spasms, visual problems, psychiatric conditions, gastrointestinal problems and so on.

But there is one remarkable difference between then and now.

Back then, everyone knew that cannabis can cause some nasty side effects. Today, astonishingly, half of Americans believe that cannabis has zero potentially serious side effects. Sorry to say, but this is the medical equivalent of believing in unicorns.

Regardless of the century, physicians throughout the ages have known that real medicines carry risks. Any truly medicinal substance is able to give a little whack to one or more bodily processes. The goal is to whack the body back into normal functioning. That’s basically what medicine is all about – strategically whacking our physiology. But anything capable of whacking (which is to say any real medicine) is capable of harming at least a few of the many patients who would take it. This fact is so non-negotiable that we have a name for doctors who claim to have discovered effective medicines that don’t have any risks: we call them quacks.

Let’s take a look at what physicians from a time untainted by politics, drug morality, or profit motive had to say about cannabis risks:

“In large doses it will produce hallucinations, which, in some, are of merriment and in others of a violent nature, even tendency to crime … Its habitual use will cause insanity.”
– Materia Medica and Clinical Therapeutics, by Fred Petersen, published in 1905

“The most common effect, however, is the development of insanities which have been known for many years … Chronic mania and dementia represent terminal stage.”
– A Textbook of Materia Medica, Pharmacology and Therapeutics, by George F. Butler, published in 1908

“Repeated use of the drug produces mental weakness and [mental] impotence, the result of over-stimulation.”
– A Compend of Materia Medica, Therapeutics, Prescription Writing: With Especial Reference to the Physiological Actions of Drugs, by Samuel O.L. Potter, published in 1890

“Sometimes the delirium induced by hemp causes the individual to do deeds of violence, but does not act upon all alike… The after-effects are those of depression.”
– Materia Medica and Therapeutics for Physicians and Students, by John Biddle, published in 1895

“Hallucinations occur, but they are not usually agreeable; they are often painful and are replaced by stupor … Not unfrequently the excitement takes the form of a furious delirium, in which acts of violence are committed – whence the name ‘haschaschins,’ or assassins, applied to the unfortunate hashish-eater who, under the influence of the drug, commits murder… Dilatation of the pupil, and disorders of vision, which contribute to the hallucinations by distortions of external objects, are produced by hemp”
– A Practical Treatise on Materia Medica and Therapeutics, by Roberts Bartholow, published in 1893

“There is often a disposition to laugh, sing, shout, or dance, or to do some other extravagant act; but, in other instances, the excitement betrays itself in a quarrelsome temper or deeds of violence… Occasionally, a species of intoxication is induced, with hallucinations or complete delirium… Among those who use it habitually, it is said ultimately to impair the mental faculties”
– A Treatise on Therapeutics, and Pharmacology, or Materia Medica, by George B. Wood, published in 1868

For the record, I’m entirely in favor of fully legal cannabis.

But legal cannabis is ethical only when the consumers are fully informed about the risks as well as the pleasures. And that does not describe our present-day situation. 49 percent of Americans unwittingly believe that cannabis is totally safe, according to this demographically-balanced national survey conducted on March 7, 2019:

The doctors from the 19th century had no reason to be biased. They didn’t have many medication options back then, so they were probably slightly biased toward seeing the good side of cannabis – it’s just that they could not in good conscience ignore to document the occasional tragedies, or to point out that these tragedies appeared more likely with higher doses or prolonged use. Moral crusades against intoxicants wouldn’t start until the 1920s. The 19th-century doctors had no reason to overstate the risks of cannabis. Coca leaf extract and opium were widely and matter-of-factly used as medicines in that era as well. It was an exceptionally psychotropic-tolerant time.

Yet there it is. Textbook after textbook from that era describes exactly what most of my psychiatrist colleagues and I have been witnessing in our emergency rooms for years. Cannabis is not safe for everyone. People need to know.

Erik Messamore is a psychiatrist and can be reached on Twitter @ErikMessamoreMD and LinkedIn.

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