Soooo if you are keen for a read

Let me define smoke and vapour first. These are my own definitions which I believe are quite accurate - chemistry is not my field though so feel free to correct or nitpick.
Smoke: Burnt particulate matter suspended in the air - material is combusted and turned into stuff floating in the air. It will not return to its original form when cooled back down to the temperature it combusted at. Specifically here I’m talking about burning plant matter. Light a leaf, it burns, you get sooty smoke.
Vapour: The gaseous form of a substance when at a temperature above its boiling point. For water, that is 100 degrees Celsius. Hydrogen is a gas at room temperature. Meth vapourises at... well... whatever temperature it is when you're heating it and it starts to look deliciously wispy %) Anyone know off-hand? When returned to a temperature below that point, it goes back to a liquid/solid. Vapour tends to be lighter, wispier, and not even visible at all at most concentrations. Water vapour is in the air all around us, and we don't see it.
So, I’m going to make the practical assumption that your meth is reasonably clean. Anywhere in this I say ‘pure’ I mean that ideally, your rock is 100% methamphetamine, or only cut with agents that act in the same way, eg MSM. If there is something in there that burns –
I’m looking at you glucose, and that delicious yet disappointing toffee smell – then what I am going to say is obviously less applicable.
Ideally, meth is a pure substance - 1g of ‘pure’ crystals is equivalent to 1g of methamphetamine (at least, this is what you are desperately hoping for when you test that new bag you just got

). Weed, on the other hand, contains a small amount of THC by weight, and when smoked most of the visible gas is useless, burnt plant matter – you inhale the good stuff with it, it gets absorbed and you can exhale the ‘dead’ smoke.
So the difference? Weed (or tobacco) smoke is not the substance you are trying to get into your system – THC or nicotine is, the visible part is smoke that just comes in and goes out as part of the process of burning the plant matter.
Because meth is a pure chemical, when you heat it up and it starts to form vapours, you are looking at the gaseous form of your target substance – not a cloud of ‘other stuff’ or smoke that contains meth. That very stuff you are so carefully trying to get into your bloodstream
is the misty cloud that you see forming in the bowl and proceed to gleefully suck down. Logically, this means that you cannot exhale ‘dead’ smoke – there is no smoke, it’s all meth vapour! Thus, this suggests that not only do your lungs take longer to absorb a hit of meth, since after a big hit and 5 or 10 seconds you can still breathe out vapour, but it brings us to the solid conclusion that
if you see vapour coming out again, it is actually meth, and you did not absorb all that you inhaled.
Now, while some people may believe that giving freely to the universe can invoke good karma, it is more likely that your cat will catch your vibe rather than the cosmos.