Ambivalent relationships are more toxic than negative ones, says Wharton psychologist: How to set limits with a frenemy

Knowing you have to see someone you just don't get along with can be anxiety inducing. But even more toxic than a negative relationship is an ambivalent one, Adam Grant, a Wharton psychologist, writes for The New York Times. 

If someone is ambivalent toward you it means they have mixed feelings about you. This might cause them to greet you with a smile one day but give you the cold shoulder the next.

"I had assumed that with a neighbor or a colleague, having some positive interactions was better than all negative interactions," he writes. "But being cheered on by the same person who cuts you down doesn't buffer the bad feelings; it amplifies them." 

Here's why ambivalent relationships can be more harmful to our health than negative ones, and how to set boundaries with those mercurial people in your life. 

"The most intuitive reason is that ambivalent relationships are unpredictable," Grant writes. "With a clear enemy, you put up a shield when you cross paths. With a frenemy, you never know whether Dr. Jekyll or Mr. Hyde is going to show up." 

That's why a frenemy can cause you more distress than a straightforward enemy, according to a 2005 study.

That stress causes adverse health effects. 

Ambivalent relationships lead to greater risk of disease, according to one 2012 study. They can also lead to higher blood pressure.

The best way to alleviate some of that stress and the downstream health affects is to set a boundary, Nedra Glover Tawwab, a licensed therapist and author of Set Boundaries, Find Peace, told CNBC Make It last year.

"Anxiety and depression are just some of the mental issues or concerns that arise when boundaries are not present in relationships," she said. "The lack of boundaries can make people feel powerless and hopeless."

Here are three steps to help you draw a line:

1. Un-learn self neglect 

"Self-neglect is not a way to show how much you care for others," she said. "In relationships, both parties can choose what they want and need."

Tell yourself that you deserve to have preferences, and don't feel bad for acting on them. 

"This can be a helpful step toward speaking your needs and desires," Tawwab said.

2. Start thinking of time as finite

Saying "yes" to spending time with someone who may or may not be nice to you means you are losing time and possibly subjecting yourself to a toxic experience.

That's why you should get comfortable saying "no." 

"Boundaries around how you spend your time and allow others to use it are essential," Tawwab said.

Let's say a co-worker who is equal parts supportive and jealous of your accomplishments asks you to lunch.  It's okay to tell them you'd rather grab a bite alone.

Or if a childhood friend who is in a particularly negative headspace asks you to dinner. It's okay to say you are busy. 

Remind yourself that there are a limited amount of hours in the day, and they should be cherished. 

3. Use 'I' statements 

When drawing a boundary, don't talk about what the other person is doing. For example, if you want to stop grabbing lunch with your co-worker, don't make it about their actions or attitude.

Instead you can say "I just need some alone time mid-day and these lunches are the only time I can get it." 

By setting boundaries with a frenemy, you can limit contact and protect your health.

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