The symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these conditions are infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages. Opportunistic infections are common in people with AIDS.[25] HIV affects nearly every organ system. People with AIDS also have an increased risk of developing various cancers such as Kaposi's sarcoma, cervical cancer and cancers of the immune system known as lymphomas.....http://en.wikipedia.org/wiki/AIDS#Symptoms_and_Complications The main health risks in tobacco pertain to diseases of the cardiovascular system, in particular smoking being a major risk factor for a myocardial infarction (heart attack), diseases of the respiratory tract such as Chronic Obstructive Pulmonary Disease (COPD) and emphysema, and cancer, particularly lung cancer and cancers of the larynx and tongue. Prior to World War I, lung cancer was considered to be a rare disease, which most physicians would never see during their career. With the postwar rise in popularity of cigarette smoking came a virtual epidemic of lung cancer.[3], [4] Incidence of impotence is approximately 85 percent higher in male smokers compared to non-smokers[5], and it is a key cause of erectile dysfunction (ED)[6] [7]. Smoking causes impotence because it promotes arterial narrowing[8]. Tobacco related illnesses kill 440,000 people per year[9], about 1,205 per day, making it the leading cause of preventable death in the U.S. A person's increased risk of contracting disease is directly proportional to the length of time that a person continues to smoke as well as the amount smoked. However, if someone stops smoking, then these chances gradually decrease as the damage to their body is repaired. Diseases linked to smoking tobacco cigarettes include: Most forms form of cancer, particularly lung cancer[10], cancer of the kidney[11], cancer of the larynx and head and neck, bladder, esophagus, pancreas, and stomach[12]. There is some evidence suggesting an increased risk of myeloid leukaemia, squamous cell sinonasal cancer, liver cancer, cervical cancer, colorectal cancer after an extended latency, childhood cancers and cancers of the gall bladder, adrenal gland and small intestine. Cardiovascular disease stroke respiratory ailments such as the common cold and bronchitis peripheral vascular disease birth defects of pregnant smokers' offspring Buerger's disease (thromboangiitis obliterans) impotence chronic obstructive pulmonary disease, emphysema and chronic bronchitis in particular More likely to develop cataracts that may cause blindness Reduced memory and cognitive abilities in adolescent smokers(Biol Psychiatry. 2005 Jan 1;57(1):56-66)[13] The incidence of lung cancer is highly correlated with smoking.Cigar and pipe smokers tend to inhale less smoke than cigarette smokers, so their risk of lung cancer is lower but is still several times higher than the risk for nonsmokers. Pipe and cigar smokers are also at risk for cancers of the oral cavity, larynx (voice box), or esophagus, a risk which was widely hypothesized before any link between smoking and cancer was scientifically proved as seen in the news coverage of the tobacco-related cancers of two American presidents; Ulysses S. Grant died in 1885 at age sixty-three after a long and painful public battle with throat cancer which was widely assumed at the time to be the result of his lifelong cigar habit, and Grover Cleveland was diagnosed in 1893 with cancer of the left jaw, which was frequently remarked upon by the press and public as the side where he usually had a cigar clamped. Similarly, cancer of the mouth and jaw is also a risk for chewing tobacco. The benefits of smoking cessation are immediate: blood pressure, heart rate, and temperature return to normal range; heart attack risk decreases; ability to smell and taste is enhanced; circulation improves. It is generally assumed that the major motivational factor behind smoking is the nicotine it contains. However, the practice of ingesting the smoke from a smoldering leaf generates an enormous number of active chemical compounds, loosely lumped together as 'tar', many of which are biologically reactive and potential health dangers. (Chewing tobacco is also carcinogenic, likely because similar compounds are generated in the practice of curing it; the Nordic snus, which is steam cured and therefore does not generate these compounds, is much less carcinogenic.) There are around 3000 chemicals found in tobacco smoke. Long term exposure to other compounds in the smoke, such as carbon monoxide, cyanide, and other compounds that damage lung and arterial tissue, are believed to be responsible for cardiovascular damage and for loss of elasticity in the alveoli, leading to emphysema and COPD. In addition, cigarettes contain 19 known carcinogens..... http://en.wikipedia.org/wiki/Health_effects_of_tobacco_smoking Increased chance of blood-borne infection — This is generally a two fold problem. One is needle sharing which transmits blood-borne diseases between users and the other is secondary infection of injection sites caused by lack of hygiene and failure to rotate the injection site. In addition, the use of cotton to filter some drugs can lead to cotton fever. Increased chance of overdose — Because IV injection delivers a dose of drug straight into the bloodstream it bypasses the body's natural chemical defenses. Taking too much can result in unpleasant side effects, some of them very serious. Scarring of the peripheral veins — This arises from the use of blunt injecting equipment. This is particularly common with users who have been injecting while in jail and re-use disposable syringes sometimes hundreds of times. Although somewhat of an urban legend that IV drug use for an extended period will result in collapsed veins, this is untrue as long as the site of injection is constantly moved and old sites are given a chance to heal. Increased chance of addiction — It is possible that the heightened effect of administering drugs intravenously can make the chances of addiction more likely but this is not established. Needle phobia — Quite a number of people have an intense aversion to needles which, in extreme cases, is called trypanophobia and can make them feel nauseous or faint. Social stigma — In many societies there is a social stigma attached to IV drug use. Many people feel that it is somehow "unclean" to take drugs in such a manner, even though they may be perfectly comfortable taking them by another route. This may be because of its common use in inner cities and with lower-class people. http://en.wikipedia.org/wiki/Intravenous_drug_use_%28recreational%29