Recently, I was reading, news about some celebrity, who was found dead in a hotel in Kampala, Uganda, probably choked by secretions in the mouth. All this happened after consuming cocaine bought from some local vendor. It was reported that he had probably taken some, "bad cocaine”.  This was probably to divert public attention from the fact that the deceased was using abusive substances.  After reading it, one should not form the impression that some good cocaine exists.Cocaine is one of the addicting substances abused all over the world.  It can be used as oral preparations or to be inhaled or injected. After use, it has a euphoric effect on the brain, making the person feel good. It causes constriction of the blood vessels of the body which can result in hypertension, nose bleed and cardiac problems. Physical tolerance to cocaine builds early, hence the user feels compelled to take it in higher doses. The dependence is therefore increased resulting in more problems.Cannabis or marijuana refers to the preparations obtained from the cannabis plant.  Hashish and marijuana are derivatives obtained from the cannabis plant. The constituents are used variously as psychoactive substances and for recreation. As per United Nations, cannabis is the most abused illicit substance world over.It has certain medicinal properties. Like it improves appetite in chronically ill patients, reduces nausea and vomiting and gives a sense of well being. But apart from this, it has many harmful effects on the body which outweigh the advantages.Cannabis influences the driving ability of a person. It is harmful for fertility of a woman.  In a pregnant woman, it is harmful for the fetus. In susceptible people, cannabis can induce psychosis. Long term use leads to memory loss and inattention. Opium is yet another substance abused since ancient times. It is obtained by collecting and drying the juice of unripe seeds of the poppy plant. Morphine, codeine and heroin are contents of this plant which are all addicting, whereas two other substances, papaverine and narcotine are non -addicting.Opium and its derivatives were widely used for its pain killer properties, as it helps to relieve severe pain as that of malignancy or after a major operation. It also gives a sense of relaxation to the mind.  But very soon its addicting properties were discovered. Even today morphine is used for severe pain but with caution. People with chronic pain have been known to become addicted to morphine.  Opium is converted to heroin as it becomes more potent in addiction and lighter in weight to transport. After regular use one craves for more and more doses which harms the body. Opium and its addicting derivatives cause dulling of intellect, impairment of judgment, somnolence and visual problems.All these addictive substances can be smoked as well.  Smoke of these drugs harms the body as much as tobacco smoke and increases risk of lung cancer.The list of these abusive substances and various addictive substances derived from them is very long. But one thing is crystal clear. All these substances damage the physical and mental health of a person in multiple ways.A person using any of these substances regularly becomes a dull and sick human being with no drive or energy to do any work.  He loses all interestsin better things of the world. The addicts also lose their appetite and often suffer from malnutrition. Overdose of these substances is often fatal. Therefore one should avoid use of these substances. If somebody has started this habit for whatever reason, it is better to nip the habit in the bud.Those addicted to these abusive substances and having desire to give up the habit can seek help from professional centers which can help them to quit this habit and rehabilitate them to become normal and healthy once again.In Rwanda, we are witnessing appreciable work in taking a very tough stance towards drug peddlers. Abusive substances are often caught and burnt. Public awareness of the dangers of substance abuse is one way of defeating substance abuse.Dr Pande is a Specialist internal medicine-Ruhengeri Hospital