[adam]

Here's some of what I had read previously on it - the refutations of it are harder to find that endorsements:

Now, there is in fact an Isma’ili sect called the Nizari that lies at the centre of the Hashashin myth. And there is also a famous leader of the Nizaris called Hassan i-Sabbah who established a stronghold at Alamut in the mountains south of the Caspian Sea in 1090. Other than building strongholds, the Nizari leader improved irrigation and cultivation and began sending religious emissaries to other Isma'ili communities spread out through the Islamic world. It is Hassan i-Sabbah that seems to be the contender for the title ‘Old Man of the Mountain’, but rather than being a drug pushing megalomaniac, he is described by one historian as “a strategist, an administrator and a thinker who led a highly ascetic life and enforced the sacred law of Islam very strictly throughout his community”. And as other historical sources suggest, the fanciful term ‘Old Man of the Mountain’, is likely to have originated from Western occidentalists, and may have been a mistake in translation, since ‘Old Man’ is the literal translation of ‘Sheikh’.

Now, it is from his stronghold in Alamut that Hassan i-Sabbah initiated a policy of armed revolt against the Seljuk rulers who were back by the Abbasid Sunni leadership in Iraq. Against the might of the Seljuk armies, the Nizaris adopted guerrilla style tactics in their armed struggle, a feature of which was the often open and spectacular assassination of religious or political enemies. But as one historian points out, they were not the inventors of the policy of assassination, nor the last group to resort to such methods, yet somehow any assassination of religious, political or military significance during the Alamut period was attributed to them.

So, it seems that on closer inspection the Nizari sect and their leader Hassan i-Sabbah were the victims of some political spin. There appears to be no evidence that the Nizari sect has ever endorsed the use of Hash or any other drug, and some writers suggested that rather than a drug reference, the word ‘Assassin’ simply stems from the 'followers of Al-Hassan'. In light of this, one has to wonder how such a fanciful story of the drug crazed Hashashin spread so pervasively. Rather than based on fact, it seems the drug association was a myth encouraged by the enemies of the Nizari. As Barnard Lewis, the famous Islamic History professor explains, the word Hashashin was “an expression of contempt for the wild beliefs and extravagant behaviour of the sectaries - a derisive comment on their conduct rather than a description of their practices”. These sentiments seem to be backed by other historians who attribute the Assassin legends not only to the general hostility of the Sunni Muslims towards the Isma’ilis and but also as a story taken up by Europeans as yet another fanciful impression of the Orient. And so ends today’s lesson in Middle Eastern mythology, hopefully you enjoyed it.