In the autumn of 2007, hospitals near Leipzig, Germany admitted 29 people after they inadvertently smoked weed contaminated with lead. Yep, some dealer or grower decided it was a good idea to drop a bunch of small lead particles into the marijuana they were selling, presumably to increase its weight (lead is super dense) and thus make mad bank. The average lead content of stashes recovered from the poisoned individuals was 10% by weight, translating into an additional ~$1500 per kg of pot sold.
It turns out the center of a lit joint can reach temperatures up to 1200°C, sufficient to ensure a bunch of lead particles will end up in the inhaled smoke and so be absorbed via the lungs (particularly if the inhaled smoke is being held in to maximize absorption of non-lead stuff like THC). Those with lead poisoning showed up to the hospitals with stomach cramps, feeling like they were going to barf, lacking sufficient numbers of red blood cells (anemia), and being unreasonably tired. Most had basophilic stippling and exhibited Burton's line (here's a gross photo), which are classic indicators of lead poisoning. One particularly unfortunate person also had their nervous system seriously damaged by lead. In addition to experiencing hallucinations, this individual exhibited wrist drop because a nerve connecting their spine with their arms stopped working properly.
Aluminum and small bits of glass have also been found in marijuana sold on the street. The aluminum was attributed to using unreasonably dirty water to grow the plants, while the glass was thought to be intentionally added to make the pot look better (like it has lots of crystals) and increase its weight. Inhaling hot glass fumes isn't pleasant since they can severely burn your mouth and lungs.
|Claviceps purpurea fungus growing on grain (Source)|
Very rarely, dropping acid (LSD) can result in ergot poisoning, which is probably one of the worst possible outcomes for a trip. If the LSD is synthesized from lysergic acid obtained from the ergot fungus (Claviceps purpurea), it may be contaminated with other toxic fungal alkaloids. Ergot poisoning (aka St. Anthony’s fire) has been around since we first began harvesting rye and other grains to eat. The fungus grows on these plants, producing a bunch of compounds that aren't very nice to the human body. They act on the intestines to produce diarrhea and on the nervous system to produce seizures. Ergot alkaloids also cause blood vessels to constrict, reducing blood (and thus oxygen) flow to the arms and legs (aka limb ischemia, usually accompanied by burning pain). In severe cases, the reduced blood flow can lead to gangrene, where the ends of one's fingers and toes to die, turn black, and eventually fall off.
Busse F, Omidi L, Timper K, Leichtle A, Windgassen M, Kluge E, Stumvoll M. 2008. Lead poisoning due to adulterated marijuana. New England Journal of Medicine 358(15):1641-1642. [Full text]
Cole C, Jones L, McVeigh J, Kicman A, Syed Q, Bellis M. 2011. Adulterants in illicit drugs: A review of empirical evidence. Drug Testing and Analysis 3(2):89-96.
Raval MV, Gaba RC, Brown K, Sato KT, Eskandari MK. 2008. Percutaneous transluminal angioplasty in the treatment of extensive LSD-induced lower extremity vasospasm refractory to pharmacologic therapy. Journal of Vascular and Interventional Radiology 19(8):1227-1230.