Etymology: Dope

I've been wondering if the term 'dope' as used in reference to drugs somehow originated from the plumbing terminology.

When connecting cast iron drainage pipes, the traditional practice is to take a strand of hemp (called oakum) and stuff it around the pipe and then pour molten lead over that. Plumbers also use the term 'dope' to mean a sealant that is used to make connections watertight. Typically the term refers to a liquid but I've heard the term used for teflon tape that is used for the same purpose.

The hypothesis: When marijuana smoking was first widely introduced to North America, the fact that it comes from the same plant as hemp lead to people referring to it as "smoking dope". This would require that the term 'dope' was commonly used to refer to 'oakum'.

This is completely a guess on my part. Is there any evidence for or contrary to this idea?

Answer

@Jim noted though EtymOnline puts forward the following theory:

1807, American English, "sauce, gravy, thick liquid," ... Extension to "drug" is 1889, from practice of smoking semi-liquid opium preparation

A guest post by Tom Dalzell on the Oxford Dictionaries blog gives further details of this:

Turning to dope in its specific drug sense: in 1886 (according to Green’s Dictionary of Slang), we first heard of a dope fiend – a drug user. A few years later, we find dope referring to opium or a morphine derivative. The link between the syrup and the drug may not be immediately obvious, but it relates to the ‘the thick treacle-like preparation used in opium-smoking’; as early as 1872, dope had referred to ‘a preparation, mixture, or drug which is not specifically named’. In 1933 we encounter dope addict. Dope eventually stood on its own, coming to mean any drug (1900) or medicine (1902).

However, whether this theory has been proved beyond doubt to be the actual origin is unclear. The blog closes with the words: "The opinions and other information contained in OxfordWords blog posts and comments do not necessarily reflect the opinions or positions of Oxford University Press."

The OED itself does not explicitly comment on how the drug-related sense of "dope" developed, but the way in which the senses are organised implies a different theory: sense 3a (1851) is a "simpleton" or "fool" (or a person under the influence of drugs, with an 1866 quote describing a "dozened" "dope", where "dozened" means stupefied or benumbed) - and sense 3b (1886) is "‘Opium, especially the thick treacle-like preparation used in opium-smoking’ (Cent. Dict. Suppl. 1909); hence applied to stupefying drugs and narcotics in general, or to alcoholic drink". The implication seems to be that the OED believed sense 3b to be an extension of 3a - in other words, it was thought that was dope was so named because of its stupefying effects. However, this isn't stated explicitly, and it isn't clear how recently the entry has been updated (it says it hasn't been fully updated since 1897, but clearly it has been updated to some extent).

It is unlikely that your theory about hemp-based sealants is the true origin, since Dalzell relates that "Dope came to refer specifically to marijuana only in 1950 (according to the Historical Dictionary of American Slang)", whereas it seems established that originally (in terms of its use as a drug reference) it referred to opium.