Germany made extensive use of stimulants, especially an oral preparation of methamphetamine known by the trade name of Pervitin (see e.g. Der Spiegel). Prolonged use, lack of sleep and combat stress would be certain to produce serious or catastrophic side-effects.

I've no specific knowledge regarding other powers, but stimulant use without the need for a prescription was common in that era. Given that drugs like benzedrine were a staple for many university students cramming for examinations, it's probable that militaries made wide use of them also.