Can a case of untreated ADHD cause major depression?

YES. Research indicates that up to 25% of untreated adhd patients can develop depression. The chronic stress associated with the symptoms of adhd can lead to depression.
ADHD and Depression. Also, self image/ self esteem issues , substance use, some medications, and genetic predisposition can be factors in developing depression.
Not directly. People with adhd suffer from the negative effects on their work and relationships at times. This can lead to low self-esteem and perhaps lead to major depression if the negative feedback persists and is severe enough. Sometimes we will see depression occurring with adhd. I've seen the combination more often than not in my practice.
Possibly. If your symptoms are really disturbing you, you could become depressed about them. Do consult a psychiatrist.
Adhd/ depression. If the adhd is causing issues with your life serious enough - it could precipitate a depression. I guess my concern is - are the symptoms that you think are adhd actually depression? Probably best to make an appointment with your family doctor.

Related Questions

How can I stop being late?!? I have major depression, adhd, chronic pain & social anxiety.

Yo need treatment. You need serious dedication for good therapy . Biofeedbsck, cognitive therapy, may be medications . You have to find the right therapist and look for solutions. Read more...
Structure/schedule. For adhd, social anxiety, and depression set a structure that is more rigid than flexible. Make a schedule for events and task completion that is visual and auditory. Record it on your phone, set alarms etc. Make it more difficult for you to avoid lateness by setting earlier reminders to leave and get ready to leave. Read more...