During or after service, did you ever have a problem with substance abuse?

Not me but my 20 and 21 year old stepdaughters currently do have been in and out of drug, pot and alcohol abuse. They did not finish High School and they did not serve in the military They had an easy life until they were kicked out our house. My Wife belongs to AA. She had a step dad , world war 2 fighter-bomber (Mosquito) pilot and alcoholic who later sobered up and got 3 Master Degrees. He believed in AA and NA. He was a High School Principal and knew how to get kids to not be drunks and druggies.
When you talked to others who have beaten drinking for 1 year or even 25, you get the strength that you did not know you had and you get the support group. Many are veterans.

http://www.aa.org/

In my twenty plus years in the military, never once did I ever get in trouble for alcohol, come close tho. If at all possible, I didn’t “party with the boys,” because I knew what I was capable of, regarding a temper and alcohol, so I started to keep to myself. Later, when I obtained enough rank to get my own room in the barracks, and later move off-post, my best friends came in 16 oz. cans. I was never late for formations, did my job well, was able to tolerate everyone…of course my friends were waiting in the refrigerator. I was a “functioning alcoholic.” During my years in the military, I was sent to ASAP in the early 90s, which like most alcoholics, I fought it! Before leaving the military, I was having trouble keeping my weight down, because alcohol, and beer have calories! When I left the military, deciding to QUIT was not an issue for me…my reasoning was, I wanted to lose weight and alcohol and beer cost money. The first 30 days of stopping was tough, and I lost several pounds right off the bat. I’m still fighting the battle of the bulge, but doing better.

https://www.ashwoodrecovery.com/blog/six-signs-high-functioning-alcoholic/

I never had issues with illegal drugs but had enjoyed my beer early in my life. I had been a smoker since five years of age and I quit that in 1965. My motivation behind stopping smoking, drinking alcoholic beverages, coffee and tea was religious-based. Without getting into the doctrinal issue that compelled my stopping those vices I had gone cold-turkey. The smoking and coffee aspect was the toughest for me to stop, but the reasons behind my wanting to do so were more compelling.
My major vice today is chocolate.