Cannabis has about 118 carcinogens when smoked, nicotine cigarettes have 70 carcinogens when smoked. A study of 1000-2000+ people in the National British Lung and Cancer foundation found that 9 percent of people who smoked 1-2 cannabis joints succumbed to lung cancer whereas 8 percent of people who smoked 20-30 tobacco cigarettes succumbed to lung cancer. Smoking weed has been linked to a significant increase of susceptibility to testicular cancers, demonstrated innumerous studies. One published article in a very respectable journal even pointed to the fact that it's likely people who smoke joints are as much as twice as likely to develop cancer of the testes. THC mimics a natural neurotransmitter found in the human brain known as cannabanoids, meaning it has direct access to wreak havoc on various networks of neurons in the brain. Due to THC being a foreign substance and yet being able to bind to cannabanoid receptors in the brain, it can induce foreign effects on the brain that evolution did not want our brain to experience. An example of this is when THC binds to cannabanoid receptors, it induces a foreign biochemical response that decreases the amount of protein kinase A, which has been linked to increased inhibition among neurons, meaning less synaptic transmission in important areas like gray matter (one of the main parts of the brain that has been atrributed to intellectual capabalities). Since weed inhibits neurons in these regions, it creates a dampening effect, which suppresses neural activity, even showing emperically observed decrease in intellectual capabilities of particapants in published studies. Because THC naturally mimics cannabanoids, the brain actually responds by releasing burts of dopamine, because the brain likes foreign substances that produce a "new pattern" of neural activity (or less activity in this case). Smoke too much constantly, enough dopamine (which is a very powerful neuromodulator that creates new neural networks or modifies pre existing ones), that new neural networks that respond to the cannabis, and when they don't get their fix of cannabis, they create havoc (this is known as an addiction). A few years ago, people didn't believe cannabis wans't a powerful enough drug to create this phenomena, but with new research proceeding, evidence suggests otherwise. Since the THC in cannabis can influence neuron activity, it's been suggested psychological studies (with emperical date backing it) that weed takes a part in causing schizophrenia in people who are predisposed to the condition. Now, it's known as an addictive substance, and the DSM IV, the BIBLE of psychiatrists and psychologists worldwide, often looked as the ultimate authority of psychological disorders, is including cannabis withdrawal and addiction as an official psychological/psychiatric phenomena in its next edition coming out in the fall. As for the whole "weed suppresses cancer" hype, it's been most recently linked to ONE chemical (cannabinol) of the 400 other chemicals (118 which are directly linked to causing cancer) and only induces its effects (that have been demonstrated so far in lab studies) in LATE stage cancer cells. In fact, scientists have extracted cannabinol solely from cannabis extracts and modifiying it to create a medication (i.e. a pill or vaccine) that chiefly uses this ONE chemical of weed to suppress cancer in patients (i.e. if created, it will lack the pleasure inducing chemicals found in regular cannabis). There's some propaganda, I mean science, suggesting cannabis is a legitimate drug, and does wreak many negative effects on the body.