Poisoning is a frequent cause of referral to medical emergencies and a major health problem around the world, especially in developing countries. We aimed to review the epidemiology and pattern of adult poisoning in Iran in order to facilitate the early diagnosis and management of poisoning. The pattern of poisoning is different in various parts of Iran. Pharmaceutical compounds were the most common cause of poisoning in most parts of Iran. Pesticide-related toxicities were more common in northern agricultural regions, whereas bites and stings were seen more commonly in southern Iran. Carbon monoxide poisoning was common in cities with many motor vehicles such as Tehran and in colder climates such as in northern and western regions due to inadequately vented gas appliances such as stoves and heaters. Majoon Birjandi (containing cannabis) is a unique substance used in eastern Iran. Poisoning by opioids, tramadol, and pesticides (organophosphate and aluminum phosphide) has remained a common hazard in Iran. Poisoning-associated morbidity and mortality rates vary by region and have changed over time due to the introduction of new drugs and chemicals. Early diagnosis and proper treatment may be lifesaving; thus, understanding the general pattern of poisoning in different regions is important.