Dear Co-It-All,

The other day I went to the movies with my 17-year-old niece. Well, technically, she is my step niece. My older sister married her dad two years ago. I am only 23, so we have always been more like friends than aunt and niece. Anyway, like I said, we were at the movies and she told me that she and her friends do MDMA. She made me promise not to tell my sister, but I feel like maybe I should.

Ugh. Thanks a lot for this question. Truth be told, I considered moving your question to the bottom of the pile because it is such a fricking tough one. At least I think it’s a tough one: On the one hand, I’m inclined to think it’s not that big of a deal. A lot of nineteen year olds use drugs, and MDMA has become a pretty popular one over the last decade (thanks a lot, Madonna).

On the other hand, if I tell you it’s okay not to say anything, and then something bad happens to your step niece—well that would be really, really awful. Maybe even tragically awful, and I wouldn’t be able to forgive myself. Sound familiar?

I’m going to cut right to the chase here and say that you tell your sister, both because you say you are close and because she is the adult. That “maybe I should” feeling you mention—that’s your conscience operating behind the scenes. Does telling make you a bit of a narc? Yes. Does it mean that your step-niece is likely to be super, super angry at you and block on Instagram? That too. And, not to make you feel worse here, but she will be justified in her rage. By blabbing to her step-mom, you are betraying her trust. And you are doing the right thing.

Unlike a lot of questions that I field here at the co-it-all (Should I Dye My Hair Pink? How Do I Get My Friend To Stop Mooching?), this is a potentially life vs. death scenario. Note, that I really don’t want to up the drama here. Life is not an after school special and experimenting with drugs is (or at least can be) part of the teenage experience. You know what else is part of the teenage experience? Making bad decisions and getting busted.

I can remember being so incredibly furious when my mom discovered empty alcohol bottles by rifling through my room when I wasn’t home. Another time she read my diary and I felt like this was grounds to call Children’s Aid for invasion of privacy.

When I think back on the story, that is the part that is so memorable and—my own teenage indignation, which felt so incredibly legit at the time and which now seems totally hilarious and ridiculous.

In other words, eventually your niece will understand that you were doing what you thought was in her best interest. Maybe she gets grounded for a few weekends (do kids even get grounded anymore?), but someday you will both be able to look back and laugh. Until then, it’s time to take the bullet and be the grown up.

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