I've used leaves (from plants in veg and bloom) in a vaporizer and found it very effective, smoking them kind-of works but you're taking in a whole lot of smoke with a very low concentration of THC - I tried it once and got a little high but also had a bit of a headache and felt rather drained. Leaves and stems work great for making butter/oil, are usable in a vaporizer (though it is cached rather quickly since there is so little to vaporize), and will give you some kind of buzz if you smoke enough of them - but that's really a last option.