"This supports Prof. Alexander's theory: When being in an extremely stressful and depressing situation like war, Heroine can lift you up.
But when you return to your happy, loving environment, you don't need the drug anymore to feel good - it's like the humans are being put in "Rat Park", a friendly and happy environment."

Please take into account that a traumatic experience and a lack of a positive experience associated with the drug consumption is indeed unlikely to condition the brain towards addiction.
Following this train of thoughts, there would be a huge gap in repsonse from soldiers, who took drugs to relax after combat and those who were primed for combat by drugs.

And if i remember right, a lot of vietnam veterans went to booze lateron.
They were pretty unlikely to have consumed alcohol in order to be more relaxed on th battlefield.