There are many, many threads on this. It comes up every year. You may want to use the Search function to review the discussions.
I think you’ll find the majority of the recommendations suggest being candid about your usage history. The military is not surprised by underage drinking and experimental drug usage. If you are honest from the get-go on medical history forms and security clearance questionnaires, you won’t have to keep track of untruthful answers when you update these forms on a regular basis in the military. Security clearance background investigations do include interviews with people who know you, and the truth has a way of leaking out. An untruth or lie by omission left in corrected until later can bring all sorts of trouble.
For the underage drinking, there is a difference between “alcohol usage” and “alcohol abuse.” Read medical history questionnaires VERY carefully to understand what is being asked for. Do not self-diagnose. Go to the DODMERB website before even starting on any medical history. Read everything in the menu items on the left, the process, the FAQs, etc. That will also help you to understand the timeline. Here on SAF, read the Stickies at the very top of the DODMERB forum. Every year, there are candidates who self-diagnose, rush through the form, omit things they should have asked parents about, or checked yes when it should have been no, and submitted, unable to edit after that.
For the drug-related questions, I recommend answering just what is asked. “Frequently” can mean different things to different people. If it was “every weekend for a period of 3 months, but not since April 2020,” that clarifies things all around. Then let the chips fall where they may.