Well shit man anybody can take the most extreme possible negative reactions of any substance and list them all out to magnify its apparent dangers. The government commonly uses this same tactic against marijuana smokers and hallucinogenic/empathogenic drug users, we call it propaganda.

Marijuana causes short-term memory loss, problems with learning, difficulty in thinking and problem solving, loss of coordination, paranoia and anxiety that could trigger panic attacks. One study even says that your risk of a heart attack quadruples after smoking marijuana. Not to mention the prevalence of lung infections among marijuana smokers.

That was fun. Let's do Caffeine (Taken from the Wikipedia): muscle twitching, rambling flow of thought and speech, cardiac arrhythmia or tachycardia, and psychomotor agitation, restlessness, nervousness, excitement, insomnia, flushed face, diuresis, gastrointestinal complaints, frequent use can lead to tolerance and withdrawals.

Alcohol: neurotoxicity, cardiotoxicity, hepatoxicity, cirrhosis, nausea and vomiting, hypothermia, hyperthermia, respiratory failure, coma, asphyxiation, cancer, dehydration, ataxia, Wernicke encephalopathy.