This patient support community is for questions related to juvenile diabetes including celiac disease, depression, diabetic complications, hyperglycemia / diabetic keto-acidosis, hypoglycemia, islet cell transplantation, nutritional issues, parenting a diabetic child, pregnancy, pump therapy, school issues, and teens with diabetes.
Drinking alcohol does not affect your blood sugar UNLESS your drink contains something sugary like fruit juice or soda. Drinking alcohol without sugary ingredients will put a hold on your blood sugar level. Therefore I never drink alcholic beverages if my blood sugar level is above 120 mg/dL or below 80 mg/dL.
Marijuana, by itself, will not affect your blood sugar. As a mind-altering substance, however (as Mr. Gatorade points out), it can make folks more susceptible to give in to temptations & to succumb to the powers of suggestion. Many folks "get the munchies" (at least that's what we called it in my college days) and think they're hungry for everything and anything in sight. For a diabetic, this can be very serious.
The double-whammy for using drugs & alcohol in a teen setting where typically a goal is to "get wasted" is that there'll be no one around who will care or will be capable to help you if your BG crashes or gets so high you can't function well.
Alcohol without sugary mixers can cause severe lows, and because the liver is busy cleaning the toxin (alcohol) out of the system, it DOES NOT work well to release glycogen as it normally does. This can make a low extemely dangerous.
It's unfortunate that so many teens feel pressure to fit in by drinking or using drugs. You sound like a sensible young person and I hope you gradually migrate to the great circles of folks who do healthier things and still have a great time, laugh a lot and are not frightened to "get caught" by what they're doing. Good luck.