Friends are supposed to uplift and encourage one another, not tear each other down. While friendships often start out well, not all of them survive the test of time. So when is it time to let go of a friendship?

Several experts shared their thoughts with the Huffington Post and revealed the tell-tale signs of a toxic friendship. The most glaring sign of a bad friend is someone who is not even willing to listen. Joyce Morley, a marriage and family therapist, said that friendship is a two-way street. If one friend is doing 90 percent of the listening, then Morley said it's high time for some changes.

"If your friend is constantly taking and not giving, at your expense, it might be time to let them go," she said. "Think of it this way: A friendship should be a reciprocated process, and each of you in the relationship should yield a return."

Another sign of a toxic friendship is not having time for one another. On the other hand, friends could be making time for one another but one or both of the friends is dreading the meeting. Irene S. Levine, a psychologist and the author of "Best Friends Forever: Surviving a Breakup with Your Best Friend," said it would be better for people to just part ways instead of making each other miserable.

"The signs that it's time to break up may be subtle, like struggling to schedule get-togethers," she said. "Pay attention to how you act when you do get together; if you feel uncomfortable and have nothing to say, it may be because you no longer share much in common. Friends often grow in different directions."

At the same time, it's unhealthy for friends to compete with one another. A little bit of competition is good, but if the competition gets intense to the point that a friend begrudges another friend's successes, then marriage and family therapist Marni Feuerman said it's time to reevaluate the friendship.

"It's a toxic friendship if you get the sense that your friend is competitive and jealous of you," she said. "A real friend would be happy for your achievements and good fortune. You want a friend to support your dreams and life goals."

On the other hand, people should be careful to distinguish criticism from constructive criticism. It's hard to be on the receiving end of judgment, but true friends will always be brave enough to correct their friend's mistakes because they want them to improve.

Robert Rowney, D.O., a certified psychiatrist and the director of the Cleveland Clinic mood disorder unit said that being supportive - no matter how hard it is - is crucial in friendships. 

"Honesty isn't always an easy thing, but it's important to your bond. Swallowing that pill and being the best friend you can by being open with them always works out better," Rowney explained.