Misconceptions

Everything is made of chemicals. Avoid saying that chemicals are "unnatural" or "dangerous."

Medicine is not strictly a scientific profession. It can be, but is not required to be. A lot of what doctors actually do is non-scientific. The art of medicine is just as important as the science. For example, simply creating the feeling that the doctor understands a patient's problem and shares the patient's values increases the likelihood of positive health outcomes. Avoid the assumption that doctors are scientists.
It can be just as dangerous to over-medicalize mental illness as it is to moralize about it. This is why recent writers like Johann Hari focus on non-medical aspects of addiction. From his popular TED Talk you might conclude that he dismisses the model that addiction is a physical medical condition. But if you read his book Chasing The Scream, you would learn that he actually accepts the medical model as part of a bigger picture, considers it mainstream in medicine, and has chosen to make a case for the significance of the social contributors to addiction. From Hari's point-of-view, the American medical system is incentivized to offer the lowest-cost quick fix (like a pill) so treating addiction as a solely medical condition can lead to oversimplified treatments that are less effective that complex, tailored treatments that consider an addict's social circumstances. His slogan, "the opposite of addiction is connection," is effective because it is memorable, however it is just as oversimplified as the purely medical model.

Everything alters the brain. Reading these words physically alters your brain by creating memories. In your writing, it is not enough to say the "repeated cocaine use alters the brain." Be specific about how the brain is altered and what the consequence is.

Every human quality we care about has a dual nature. On one hand its character is limited by biology and the laws of physics. And on the other hand its experience is shaped by culture and personal experience. Thinkers who amplify the importance of biology in shaping behavior are making essentialist arguments. Thinkers who focus on the culturally constructed nature of a human quality are making constructivist arguments. It is important to study and understand the essential and constructed qualities of such concepts as gender, intelligence, athletic ability, extroversion, honesty, mental illness, etc. By separating "nature" from "nurture" we can learn how each contributes to the total phenomenon. But by taking either position, without acknowledging the role of the other, ignores the complexity of reality and leads to weak models. Avoid such overly simplifying models in your own thinking and question them in others.

Avoid the words "prove," "proven," "proof," etc. Outside of mathematics, nothing is actually "proven" in life. Instead of writing, "It's been proven..." try "It's been observed..." or "Scientists have support for the theory..."

Wikipedia has a great list of common misconceptions on many other topics.

A Guide To Critical Thinking