For obvious reasons, drug companies make very sure that their positive studies are published in medical journals and doctors know about them, while the negative ones often languish unseen within the FDA, which regards them as proprietary and therefore confidential. This practice greatly biases the medical literature, medical education, and treatment decisions.
In other words, the Texas Marksman's Fallacy.
There is an even more startling finding in one of the books reviewed here (Kirsch). Patients in a double-blind placebo study knew they were getting the real drug, and not a placebo, because of the side-effects. When given another drug with side effects, as a placebo, the difference in effectiveness between the real drug and the placebo disappeared! Unbe-fucking-lievable.
According to another author, Whitaker, reviewed here,
the natural history of mental illness has changed. Whereas conditions such as schizophrenia and depression were once mainly self-limited or episodic, with each episode usually lasting no more than six months and interspersed with long periods of normalcy, the conditions are now chronic and lifelong. Whitaker believes that this might be because drugs, even those that relieve symptoms in the short term, cause long-term mental harms that continue after the underlying illness would have naturally resolved.