That’ll be from the tobacco in the spliff
You can vape or just smoke pure cannabis - no tobacco needed. Or you can dissolve it into butter (THC and CBD are fat soluble, which is why cannabis takes so long to be excreted from the body) and use it in cooking.
However inhalation is preferred as it's much easier to titrate a consistent dose (it's possible to stop before the psychoactive effects start) which is better for pain and spasm management (my use). Also cooking and smoking cause different cannabinoids to be released.
Speaking of cannabinoids, all drug tests can only look for metabolites of the substances - not the substances themselves. If you ever test positive for opiods remember to tell the tester that you like poppy seeds.
(Some US companies did try to ban their employees from eating poppy seeds for this reason).
The level of spite on this thread from some is shocking. Coming from an online community that generally guffaws and 'arfs' along with jokes about wine o'clock
Is alcohol a drug ? (answer: yes). And tobacco ? (answer: yes). Personally I wish the government banned both in order to be consistent, rather than perpetuating the ludicrous hypocrisy of the war on "drugs". I imagine quite a few posters here have had to explain to their DC at some point why tobacco - which still kills thousands of people in the UK every year is legal, whilst cannabis is illegal.
Oh, and coffee, tea and chocolate are all "drugs" - non-nutritional substances which affect the endocrine system (and which are often consumed for exactly that reason).
I've been growing cannabis for over 10 years (thanks to a fantastic online community in the UK ....). I'd never describe myself as an expert. But I'm pretty good at it - as well as harvesting, trimming, curing, and preparing.