To deal with toxic people effectively, you need an approach that enables you to control what you can and eliminate what you can't.

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Toxic people defy logic. Some are blissfully unaware of the negative impact that they have on those around them, and others seem to derive satisfaction from creating chaos and pushing other people's buttons. Either way, they create unnecessary complexity, strife and, worst of all, stress.

Research has found that stress can have a lasting, negative impact on the brain. Exposure to even a few days of stress compromises the effectiveness of neurons in the hippocampus, which is an important brain area responsible for reasoning and memory. Weeks of stress cause reversible damage to neuronal dendrites (the small "arms" that brain cells use to communicate with each other), and months of stress can permanently destroy neurons. Stress is a formidable threat to your success -- when stress gets out of control, your brain and your performance suffer.

Related: 6 Effective Tactics for Handling a Toxic Boss

Most sources of stress at work are easy to identify. If your non-profit is working to land a grant that your organization needs to function, you're bound to feel stress and likely know how to manage it. But it's the unexpected sources of stress that take you by surprise and harm you the most. And those sources can be bosses, coworkers and clients. Whether it's negativity, cruelty, the victim syndrome, or just plain craziness, toxic people drive your brain into a stressed-out state that should be avoided at all costs. The Whitehall II study, which followed over 10,000 subjects for 12 years, found that people in toxic relationships had an increased risk for experiencing heart problems, including fatal heart attacks, than people who were in healthy relationships.

Related: 13 Habits of Exceptionally Likable People

While I've run across numerous effective strategies that successful people employ when dealing with toxic people, what follows are twelve of the best. To deal with toxic people effectively, you need an approach that enables you, across the board, to control what you can and eliminate what you can't. The important thing to remember is that you are in control of far more than you realize.

Here are methods that successful people use to keep other people's behavior from affecting their work and happiness.