I'm not talking about levels from the 1960's, an era so long ago that it's hardly relevant for today's practices or policy. What I'm talking about is the last 2 decades or so, a time over which use has spread further than it ever has (note: I don't make any moral judgements on that, I'm just observing), and over which cannabis production has become so far developed that the advances over that time dwarf the progress that was made over the millennia before it.

There is hard evidence that THC content (to use that as 'the' indicator for cannabis potency, which is an internationally accepted practice) has risen steadily from the mid-1990's, with a topping off in the last few years at around 15-20 % for high-potency Dutch weed varieties, and 5-7 % for imported (international) varieties. See e.g. [1] (from Wikipedia) and [2] (in Dutch) from the Dutch agency who monitors exactly this. There is little reason to believe that THC content across the world in places where they import from the same places as Dutch import would be different from the content measured in the Netherlands; international measurements confirm this hypothesis.

I know it is popular amongst 'stoners' to deny that THC content has risen, mostly because it causes marijuana to be reclassified as a more 'dangerous' (therefore: punished harsher) drug as it once was in some places. It's not because something has undesirable (for you) policy implications, that it's not true. You (not specifically 'you you', but the 'cannabis always had high THC / the Indians did it 1000 years ago' crowd) have elaborate theories but suspiciously little data on their claims. Anecdotes by 'stoners' don't make accounts of the truth, the scientific method does.

Claiming that high-potency cannabis varieties are 'just modified varieties that existed for 1000's of years' is true in the same sense that saying a Ferrari is just a modified version of a Model T. It evolved from the same thing, but the differences in potency, ease of use, yield and ease of growing under clandestine circumstances are vast. I'm not using 'Dutch' in the nationalistic 'look at how awesome we are' sense (I'm not even Dutch), I use it in the internationally commonly accepted parlance meaning 'purified by high-tech and directed selection into a product that has no equal in the world'. There is a reason Dutch users look with a mix of amusement and pity at Americans who fill a whole joint with pure Mexican low-grade cannabis and still don't get the same effects as a Dutch joint that contains mostly tobacco and only a relatively low amount of cannabis.

Lastly, I'm not using 'knocked out' in the regular (meaning 'unconscious') sense, but in the drug-using sense, i.e. Cheech & Chong style stonedness. Of course, it's true that different users have different tolerance levels, and that long-time users do build tolerance, but consuming 1 gram of high-quality Dutch marijuana is not 'recreational' use; if I were to make an analogy with alcohol, it's similar to a wild night out binge drinking, not 'sipping a glass of wine on a summer evening'. You say you're using 'high quality' but without numbers, it's impossible to gauge how 'high quality' it really is (in fact, if your hash is similar to other hash world wide, it's roughly the same as the average Dutch marijuana at around 15-20 % THC; for comparison, hash made from average-grade Dutch cannabis varieties ('average-grade Dutch' meaning 'still better than the best international varieties') varies between 20 and 40 (!) percent THC content, approaching THC levels of cannabis oil, which has always been classified as a hard drug, even in the Netherlands).

To frame the discussion further, I'm pro legalisation, and against the current direction in the Netherlands to further clamp down on coffee shops, selling to foreigners, prohibiting psylocybin mushrooms etc. I have at least 10 coffee shops within walking distance from my house, I pass by some every day while walking my kids to day care, and I'm a first-hand witness of the negative effects in terms of nuisance and street crime that the recent curbing of sales to international buyers has brought. I'm as much in the pro-lax-drug-policies as you can be without being an anarchist, but denying that THC content and marijuana potency has risen over the last decades is plain self-delusion.

[1] http://books.google.nl/books?id=mxP_duKXb7QC&pg=PA14&redir_e...
[2] http://www.trimbos.nl/webwinkel/productoverzicht-webwinkel/a...