My sister has asked to borrow quite a bit of money from me to open up a restaurant with her husband. I am inclined to loan her the money because I think she is talented and experienced and also because she is my little sister. When she and her husband came to ask for the money they also told me that her husband was on methadone and that he had been for 10 months. They said it was not a big deal but that they didn’t want me to find out from someone else after the fact and think that they had been hiding it to get the loan. I guess he got addicted to painkillers after back surgery a few years ago. I never knew that it was a problem but I guess it got pretty bad for a while. Anyway, I don’t know much about methadone. If he has been OK for 10 months does that mean he is going to be OK for ever, probably? I know that you cannot give guarantees but do you think it is likely going to be a problem for them in this upcoming business venture, considering that he has been clean for almost a year now already.
You're wise to note that there are no guarantees - in addictions, in business ventures, or in life for that matter. I would say your brother in law is off to a great start - I wonder what else he is doing to promote his sobriety/recovery other than taking methadone.
The hallmarks of recovery are accountability and responsibility - if you're seeing those from him then my best advice would be to listen very closely to your intuition and to protect yourself by formalizing a business contract. I'm not sure how close you are to the situation geographically and relationally - I'd encourage you to be vigilant and supportive.