A (not so) Troubling Correlation

This graph correlates the number of emergency room mentions of marijuana (where someone admits to smoking weed when hospitalized) with the potency of seized cannabis (the strength of the weed).

First, correlation is not causation. This does not prove that increases in potency result in more frequent medical emergencies. This graph demonstrates two facts.

One: From 1988 to 2003, the number of emergency room patients who admit to using marijuana has generally increased.
Two: From 1988 to 2003, the percentage of THC of samples of marijuana seized by drug enforcement officials has generally increased.

The obvious tactic of anti-legalization advocates is to link these phenomena in an attempt to justify their enforcement efforts. Their narrative is a relatively simple one, but its powerful in its stupidity...I mean simplicity. Basically, weed is getting stronger. At the same time, more people taken emergency room are using weed. Therefore, weed puts people in the hospital!

Some obvious criticism:

1. More people are admitting to using marijuana. This suggests that more of them are smoking, but does not prove, or even convincingly suggest, that the number of people adversely affected by marijuana has actually increased.
2. Although the trend is generally an upward one, there are numerous points where the correlation does not match up.
3. The potency trend shows that the samples police can get their hands on has increased. Once again, measurements of these samples cannot prove that rates have absolutely, across the board increased, it can only suggest it, weakly.
4. Finally, the potency trend is the only other measurement on the graph. The graph doesn't account for any other variable, or any other possible cause behind the spike in marijuana confessions.
   

It's time for drug enforcement officials, like Dr. David Murray, chief scientist of the Office of National Drug Control Policy, to stop touting these spurious correlations as causitive facts.