How to lower alcohol tolerance?

Exactly what the title says. Over the past two years of drinking in college, I have developed the tolerance of a horse. I got to the point where ten drinks did barely anything for me besides cause a hangover in the morning. I just got off of a thirty day break from drinking, and I feel like my tolerance has gotten a bit lower, but not nearly as low as I wanted. Is it possible that I have permanently wrecked my alcohol tolerance? The thought of never being able to get drunk again honestly makes me sick to my stomach. Please help!