lowest grade stuff is the hashish resin; the stuff that looks like oxo cubes. you will gain a good effect from it, but its price matches its quality; ie. both are low.
grass is the next step up, but if it is dark coloured and brownish, it too is the lowest quality ‘floor sweepings’. it will likely contain a high proportion of twig and branch material. again, it will do the trick, but the quality is quite lamentable and medicinal effect is potentially variable.
skunk / super skunk etc are the high end cannabis products; usually very fresh and potently stinky. it should feel sticky or even moist to the touch and will invariably be covered in crystal like granules. the colour of the leaf will be a vibrant green occasionally with flecks or red or purple, (depending upon the strain of plant material). this is the stuff vilified as the ‘gate way, class-A, reefer madness drug’. It is not cheap.
with all things considered, you will not die from cannabis use but you will more than likely derive some beneficial effects from it. i have witnessed first hand, the pain relief and well being it gives to those with MS or undergoing therapies for cancer. that it remains illegal in this day and age, is a damning statement of legislative apathy and little more. it is the plant which has been cultivated for the longest time by the human species; we are talking caveman stylee (for food, fuel and fibres)!!!
if placed in the situation of needing some ‘herbal relief’ i would opt for the highest quality skunk variety that I could get my hands on and simply use less of it. A nice cup of tea before bed time can potentially provide 48 hours of relief. You will likely sleep through the initial ‘stoned’ phase and wake up the next day wondering why all the fuss. The lower quality stuff will be ‘cut’ with crap, but I have never heard of a scenario where other compounds (cocaine, opium, ecstasy, amphetamine etc) were added secretly.
But yes, it is illegal and thus will be procured from a ‘criminal’. And yes, there is evidence that sustained / heavy use can exacerbate the mentality of anyone predisposed to paranoid / schizophrenic tendencies.