Dear {Recipient},
I am writing to you today because I am making amends to people I have harmed as a result of my addiction to{substance}. Specifically, I know that I harmed you by {state action}. For this, I am deeply sorry.
I know that sometimes apologies are more of a burden than a blessing, but I would like the chance to apologize to you in person. This will allow us to discuss how I harmed you and what I can do to make things right. If you do not feel that you wish to forgive me, or you do not wish to have any contact with me, I understand. However, please know that I am deeply sorry for what I have done to you and would like to do whatever I can to repair our relationship.
If you would find it acceptable for me to make amends in person, please contact me at {phone/email}. Otherwise, rest assured that this letter will be my only attempt to contact you, because I do not wish to impose on your life.
Sincerely,
{Sender}