Mutating from a novelist into a historian is a surprising and by no means natural process. In the beginning, I did not even question whether I could write a book about drugs in Nazi Germany, despite my not having a professional background in history. The only thing I wondered was, would I enjoy it?

Once I immersed myself in the archives, I felt an immediate thrill. I read extraordinary documents that detailed heavy drug use at all levels of the Nazi army and government, and realised that this had not been widely discussed before. And when I actually got down to writing Blitzed, I felt relieved. I joyfully navigated my narrative within this tightly framed genre and for once spared myself from wandering endlessly through the infinite terrain called “a novel”. Little did I know what I was getting myself into.

Especially when I took a swing at Hitler. This had in fact been my main source of enjoyment while writing; discovering that the so-called Führer took hard drugs, especially opiates, and was not quite the teetotaller that Nazi propaganda liked to portray. Hitler was not even a vegetarian – he mainlined pigs’ liver extracts and swallowed capsules filled with bulls’ testicles. These are the simple facts, and I dutifully wrote them down. At one point, while sitting in a cab in Paris, I realised that I probably had an intimate knowledge of the mustachioed monster that no one else possessed. I never wanted this, it just happened.

Then came trouble. I had poked into a hornets’ nest, mistaken a shark pool for a bathtub. I had little anticipated just how diligently historians guard Hitler’s image! I was put on trial by none other than the British historian Richard J Evans, who reviewed Blitzed in the Guardian. While chasing me away from the fortress of official Hitler interpretation, he also said something dangerous: that I “excused Hitler and the Germans for their terrible crimes”. That, according to Evans, was why the book was successful in Germany.

But I don’t say that anywhere in Blitzed – that would be a truly disgusting thing to assert. And why, then, is the book also so successful in countries that suffered so much under Nazi terror: Estonia, France, Russia, Denmark, Norway, Holland, Poland, the Czech Republic, or any of the other 20 countries, including Israel, where the book is translated? And what about the UK? Is the whole world into whitewashing Hitler? I don’t think so.

I don’t know if Evans is oversensitive about this topic, or whether he did not understand how drugs can affect a person. Did he misunderstand my book, or does he really believe that it is irrelevant to our understanding of the war that, for example, 35m methamphetamine tablets were issued to boost the Wehrmacht’s performance during the invasion of France? Perhaps what made him so angry was that a non-historian dared to rewrite history.

Luckily, there is more than one door to the palace. Other historians, including Ian Kershaw and Antony Beevor, were more forthcoming, with some examining my photocopies from numerous archives in Europe and the US. The late – and truly great – Hans Mommsen, Germany’s leading historian of National Socialism, was one of them. Sitting under an impressive bust of Goethe in his office, we discussed my findings from the archives of the former concentration camp, Sachsenhausen. The German navy had tried to develop a wonder drug to keep their soldiers awake and operational for up to five days at a time in their newly built mini-submarines, so that they might sneak up the Thames estuary and torpedo British and American ships.

The tests for this supposed miracle drug were conducted in Sachsenhausen. Inmates who had been sent to the Shoe Runners’ Commando (a penalty unit that had to test soles for the German shoe industry) were given various combinations of hard drugs – cocaine, meth, opioids – and forced to walk in a large circle, carrying rucksacks filled with stones. They started at 8pm, went on for the entire night, into the next day, and then for two more days.

Mommsen was shocked; he knew so much about the Third Reich, but had never seen the navy’s files documenting these abominable tests. “I have never heard of this,” he said, baffled. “We historians have no idea about drugs. So we have never looked this way.” Blitzed is a missing piece of the puzzle, he said. “It changes the overall picture”.

I have learned that nonfiction can be quite adventurous, even rebellious, to write. And is this not the very essence of literature? If Blitzed has taught me one thing, it is that going from novels to writing history is not a painless process, but it is certainly an eye-opening one. My next book, by the way, will be a novel.

Extract

Pervitin made it easier for the individual to have access to the great excitement and ‘self-treatment’ that had supposedly gripped the German people. The powerful stuff became a sort of grocery item, which even its manufacturer didn’t want to keep stuck just in the medical section. ‘Germany, awake!’ the Nazis had ordered. Methamphetamine made sure that the country stayed awake. Spurred on by a disastrous cocktail of propaganda and pharmaceutical substances, people became more and more dependent. The utopian ideal of a socially harmonised, conviction-based society, like the one preached by National Socialism, proved to be a delusion in terms of the competition of real economical interests in a modern high-performance society. Methamphetamine bridged the gaps, and the doping mentality spread into every corner of the Reich. Pervitin allowed the individual to function in the dictatorship. National Socialism in pill form.

More about the book

It is not hard to see why Hans Mommsen was fascinated by Ohler’s research. He was the leader of the functionalist school, which believed in the chaotic nature of the Nazi regime and that Hitler was a “weak dictator”. Nothing seems to demonstrate this better than Hitler’s drug addiction. Ohler’s book may well irritate some historians; he makes flippant remarks and uses chapter titles such as “Sieg High!” and “High Hitler”. But as Ian Kershaw, the great biographer of Hitler, has recognised, he has written “a serious piece of scholarship”, and one that is very well researched. – Antony Beevor, New York Review of Books

Buy the book

Blitzed is published by Penguin Random House at £8.99 and is available from the Guardian Bookshop for £7.64