Yup...Aluminium oxide (the stuff that is produced from heated aluminium) is toxic.
I know this from my time in a metal-fabrication workshop.

The welders have to wear face masks, and are required to have milk provided by the company (I think the milk acts as a counter to the oxide).
Obviously you're not gonna get the same amount of oxide from the can as a welder would from fabrication, but the principle is the same.
The reason you feel 'higher' from cans, is because of the toxidity.

I used cans in the early days too, but I don't think that cans are the same as they used to be (ie, more recycled material content).

Get a proper pipe, init...or smoke joints...