help, consider looking at transcranial magnetic stimulation (TMI) as an alternative to EST.
Hope this helps.
Thanks for asking and best of luck to your son!
Dr. Bruce Levine
You do not say what kind of treatment your 18 year old son is undergoing, i.e., psychotherapy, medication management with a psychiatrist etc. There is not just one cause of depression. Neither is there a "normal duration" of treatment.
Depression could be situational (e.g. a loss), environmental (e.g. being bullied), genetic (e.g. familial), and/or physiological (e.g. related to a health problem). As there are different causes, so there are different modalities of treatment.
So the person providing treatment, for depression to your 18 year old son, would be the one to ask your question as they would have done a thorough evaluation before starting the treatment and will have a better idea.
There are some books that may be of help such as "Feeling Good" by Dr. David D. Burns, "Sugar Blues" by William Duffy, "the Mindful Way through Depression" by Mark Williams, John Teasdale, Zindel Segal, and Jon Kabat-Zinn.
Wishing your son a speedy recovery and a healthy life free of depression. Take care.
Statistically speaking, medication alone is not as effective as when it's paired with counseling and if you could only choose one, counseling is more effective and more likely to produce long term benefits. Certainly, if you do not (and he does not) see any improvement within 4-6 weeks, I'd suggest discussing your options with your providers.