Did you know that one in three people who have been diagnosed with ADHD also have depression or have experienced a depressive episode? Depression causes a person to feel sad, irritable, and empty, and lasts for an extended amount of time.

It’s estimated about 18.6 percent of adults are affected by both ADHD and depression. The symptoms of depression include the loss of interest in familiar activities, feeling tired a lot of the time, and experiencing unplanned changes in sleep and eating habits. Some people struggling with depression describe feeling numb to their own life, disconnected from others, and alone even when they are not. They may also feel agitated, with a sense of wanting to get out of their own skin.

Depression is different from the “blues,” or sadness that follows the end of a relationship or a period of grief after a loved one dies, although those can turn into depression if they last for the long term.

“Sometimes with situations like bereavement, a breakup, or a job loss, it can snowball into a clinical depressive episode,” says Roberto Olivardia, PhD, a clinical associate at McLean Hospital and lecturer in psychology at Harvard Medical School. Dr. Olivardia is a member of CHADD’s Professional Advisory Board. “So, if someone notices after about a two-week period that these symptoms are still happening, then they should definitely be talking to someone.”

For some people, depression and ADHD just happen to coexist, but for others, depression is a result of ADHD, with low self-esteem and a poor self-image caused by ongoing feelings of being overwhelmed by life due to ADHD symptoms. The college student who struggles to finish a history paper worries how he’ll be able to hold a 40-hour-a-week job, pay bills, and raise a family someday, for instance. Or the young parent who is juggling work, family, and personal lives and feels she can’t do anything in those lives well.

“Part of treatment is to help them understand that it doesn’t necessarily work that way, that sometimes it could be easier to do the job that you love to do, than the history paper that you might despise. It’s not linear in that way, but it’s understandable,” says Dr. Olivardia. Similarly, it’s easy to understand why a man in his early 30s who has already been divorced three times due to the problems caused by his ADHD symptoms begins to feel worthless and then sinks into depression.

At the same time, Dr. Olivardia says he often sees people who have been misdiagnosed with depression when, in fact, what they have is ADHD. The two conditions are often mistaken.

“I’ll have patients who just have ADHD who say, ‘I wonder if I’m depressed because I feel this emptiness or sadness sometimes,’ and I’ll ask them if that’s true across all different situations,” says Dr. Olivardia.

One of the hallmarks of depression is a consistent loss of interest in activities the person once enjoyed. When his patients reply that they only feel that melancholy when they’re understimulated or bored, but that their moods change when they move on to an activity they enjoy or get involved in something with friends, Dr. Olivardia says he knows that they are not dealing with a clinical depression. Dr. Olivardia explains that that feeling could be related to their ADHD, giving the example of someone who once devoted a lot of time to playing piano but then stopped doing so.

“The question is, did you lose interest in it because of a mood issue, or did you just get bored with it, and then went on to something else?” Dr. Olivardia says. “That’s very common for people with ADHD—it’s really not due to mood as much as it’s due to a loss of stimulation or a loss of interest.” Depression is more internally focused, he says, while ADHD behaviors are more a response to external happenings. The same is true of difficulty with eating or sleeping, both of which are signs of depression but are just as common to people with ADHD. The key is whether any of those behaviors are out of the ordinary.

It’s not just depression—47 percent of people with an ADHD diagnosis also have an anxiety disorder. Many people also contend with addictive disorders, engage in self-harm such as cutting, or struggle with learning disabilities. Research has also found that children affected by ADHD are often at risk of physical or sexual abuse, or both. Any of these can be part of the long-term mood issues that turn into depression.

In addition, several studies show people diagnosed with ADHD who are depressed are at risk of attempting to or taking their own life five times more than people who are depressed but do not have ADHD. And, like a lot of behavior related to ADHD symptoms, many of those attempts at suicide and deaths by suicide are impulsive.

Dr. Olivardia strongly recommends that anyone who is being seen for any clinical psychiatric purpose should also be evaluated for ADHD, which he says is much more common than people think. It also affects what the original diagnosis will look like. For instance, Dr. Olivardia says if he is treating someone who has been diagnosed with obsessive-compulsive disorder, “when I know that they also have ADHD, I know the OCD will look different than in the patient with OCD who does not have ADHD.”

Many kinds of treatment for depression or ADHD work equally well with the other. Cognitive behavioral therapyis an effective way to treat mood disorders and emotional regulation, as well as executive functioning skills. Many people find adding mindfulness techniques can be a helpful support for treatment. For some people, stimulant medications can help too, by improving their executive functioning. However, medication isn’t effective for everyone, cautions Dr. Olivardia.

“I’ve had patients who are depressed who can’t take a stimulant because when they do, the agitated symptoms that they get around their depression increase—it almost gives them more juice and they’re better able to focus on their depressive thoughts,” he says. Those individuals might do better with an antidepressant medication, coupled with either behavioral treatment or a nonstimulant medication for ADHD. For many people, establishing a crisis plan with their mental health provider will also be essential to their well-being.