You may claim the exemption for you son if he does not earn more than $3,650. You can generally include medical expenses as a deduction for anyone who is your dependent at the time the expense was incurred or paid. Treatment for addiction qualifies.
Remember, you must itemize to take medical deductions AND you only get the amount that exceeds 7.5% of your Adjusted Gross Income as a deduction.
Good luck with this situation.
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