My first stint in the army was 1969-1973 and though never went to Viet Nam our unit in Germany was rife with drug use, progressively getting worse in 71-72 as many 'Nam vets were re-incorporated into the unit and the anti-war/anti-soldier civilian attitude had reached its peak both at home and abroad. My estimation was 70-75% of troops (rank immaterial) at least tried some form of illicit drug on a casual basis and perhaps 25-40% used it on a regular basis. However, most illicit drug was use was in the form of hash or weed with about 1-2% of personnel using harder drugs (LSD, heroine, etc.). In most instances the people using illicit drugs on a regular basis were primarily REMFs (cooks, clerks, other rear area ash & trash types) whereas the in the line Cav troopers would contend themselves to getting high on weed or actually the drug of choice, alcohol but seldom during duty hours. Our mission as a inter-border cavalry recon unit gave us a real mission so perhaps the basis for comparison with the army in general is a bit skewed as the officers & NCOs were some of the more dedicated in the service at the time and this filtered down to the rank and file as well. By '72 not only had the draft been eliminated for all practical intents and purposes but the Army had instituted a pretty regular drug testing program and many casual users just simply gave up using illicit drugs to avoid its repercussions should they intend to stay in the Army or make rank, but alcohol consumption was still a pretty common escape mechanism. Having been in the army for 30+ years and associated with vets even when I was not, I can say with a certain degree of certainty that there drug use was certainly a problem in for forces in Viet Nam but from my discussions with vets (and we're pretty frank with each other about our experiences), the majority of drug use was with weed/hash and usually on a casual basis, though at times perhaps prolonged intensive use. The use of hard drugs has certainly been noted for rear area personnel (and by draftees) at a much higher rate than by front line personnel no matter where they served. As my buddy (and senior NCO & occasional pot smoker) had once said, "If on mission & I found a guy high on hard stuff, I would have taken him out myself". (BTW when I first met him he was a PVT E2 with 11 years in the Army, 3 tours of Viet Nam, a Silver Star, 2 Bronze Stars for Valor, 4 Purple Hearts and had previously been a Platoon Sergeant - It wasn't his use of drugs that got him busted, but his Platoon Leader had a busted jaw and spent 6 weeks in a hospital).