Can I, legally, get in trouble?

Presuming you are in a public school, that is a sticky question, actually. Legally, you have the right to say whatever you want to say. But, since it is a public school, they have the right to censor your message, and could call your action insubordination.

If you do do it, I recommend the following...

Do it anonymously - dont just omit your name from the brochure, but don't brag to anyone about doing it, and try to place the brochures without being seen (although, if they have security cameras, that may not be possible).

Make sure the information can be 100% backed up, cite your sources in foot notes or include a bibliography. Sources should be from peer reviewed journal articles.

Yes, you could get in a lot of trouble. It's legal for you to print up brochures. And your brochures can say almost anything you want. But handing the brochures out at school, that will get you in trouble. Imagine the chaos if we just let anyone hand out brochures to high school students.

You can ask for permission. Who knows, your principal might say yes.

When it comes to marijuana, there are very few medical facts. I wish there was. But there's very little research.

Consider your words and actions carefully.

While you are in your legal first amendment rights, your school could have policy against your brochure and its contains... Especially if it sounds like you're saying anything at all positive about an illegal drug. Most schools have a zero tolerance policy about drugs of any sorts (legal or illegal) and you could face detention or suspension with disrupting literature says more or less that "they're not that bad."

When it comes to the "facts" about marijuana, most are biased one way or the other. Is this soapbox worth it?

No. As you stated it is your first amendment right

Yes, you are well within your legal rights to do so.