Study notes on Human Health and diseases

  • Health could be defined as a state of complete physical, mental and social well-being.
  • Health is affected by

(i) genetic disorders : deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth

(ii) infections and life style including food and water we take, rest and exercise we give to our bodies, habits that we have or lack etc.

  • Health also increases longevity of people and reduces infant and maternal mortality.
  • Balanced diet, personal hygiene and regular exercise are very important to maintain good health.
  • When the functioning of one or more organs or systems of the body is adversely affected, characterised by various signs and symptoms, we say that we are not healthy.
  • This means have a disease.
  • Diseases can be broadly grouped into infectious and non-infectious.
  • Diseases which are easily transmitted from one person to another, are called infectious diseases.
  • Some of the infectious diseases like AIDS are fatal.
  • Among non-infectious diseases, cancer is the major cause of death.


  • Bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man.
  • Such disease causing organisms are called pathogens.
  • All parasites are pathogens as they cause harm to the host by living in (or on) them.
  • The pathogens can enter our body by various means, multiply and interfere with normal vital activities,resulting in morphological and functional damage.
  • Pathogens have to adapt to life within the environment of the host.
  • Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings.

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  • They enter the small intestine through food and water contaminated with them.
  • Then migrate to other organs through blood.
  • Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite are the common symptoms of this disease.
  • Intestinal perforation and death may occur in severe cases.

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  • Typhoid fever could be confirmed by Widal test.

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  • Mary Mallon was a cook by profession and was a typhoid carrier who continued to spread typhoid for several years through the food she prepared.
  • She was nicknamed Typhoid Mary.
  • Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs.

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  • The alveoli get filled with fluid leading to severe problems in respiration.
  • The symptoms of pneumonia include fever, chills, cough and headache.
  • In severe cases, the lips and finger nails may turn gray to bluish in colour.
  • A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person.

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  • Rhino viruses cause one of the most infectious human ailments, the common cold.
  • They infect the nose and respiratory passage but not the lungs.
  • Symptoms are nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc.

It usually last for 3-7 days.

  • Droplets resulting from cough or sneezes of an infected person are either inhaled directly or transmitted through contaminated objects.
  • Some of the human diseases are caused by protozoans too.
  • Plasmodium, a tiny protozoan is responsible for Malaria.

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  • Different species of Plasmodium (P. vivax, P. malaria and P. falciparum) are responsible for different types of malaria.
  • Malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal.


  • Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles
  • The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture.
  • It releases toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days.
  • When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development.
  • The parasites multiply within them to form sporozoites that are stored in their salivary glands.
  • When these mosquitoes bite a human, the sporozoites are introduced into his/ her body.
  • Malarial parasite requires two hosts, human and mosquitoes to complete its life cycle.

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  • Entamoeba histolytica is a protozoan parasite in the large intestine of human which causes amoebiasis (amoebic dysentery).


  • Symptoms of this disease include constipation, abdominal pain and cramps, stools with excess mucous and blood clots.
  • Houseflies act as mechanical carriers and transmit the parasite from faeces of infected person to food and food products, hence contaminating them.
  • Drinking water and food contaminated by the faecal matter are the main source of infection.
  • Ascaris, the common round worm and Wuchereria, the filarial worm, are some of the helminths which are known to be pathogenic to man.
  • Ascaris, an intestinal parasite causes ascariasis.
  • Symptoms of these disease include internal bleeding, muscular pain, fever, anemia and blockage of the intestinal passage.
  • The eggs of the parasite are excreted along with the faeces of infected persons which contaminate soil, water, plants, etc.
  • A healthy person acquires this infection through contaminated water, vegetables, fruits, etc.


  • Wuchereria (W. bancrofti and malayi), the filarial worms cause a slowly developing chronic inflammation of the organs usually the lymphatic vessels of the lower limbs.


  • There they live for many years.
  • The disease is called elephantiasis or filariasis .


  • The genital organs are also often affected, resulting in gross deformities.
  • The pathogens are transmitted to a healthy person through the bite by the female mosquito vectors.
  • Many fungi belonging to the genera Microsporum,
  • Trichophyton and Epidermophyton are responsible for ringworms which is one of the most common infectious diseases in man.


  • Appearance of dry, scaly lesions skin, nails and scalp are the main symptoms of the disease.
  • These lesions results in intense itching.
  • Heat and moisture help these fungi to grow.
  • They grow fast in skin folds such as those in the groin or between the toes.
  • Ringworms are generally acquired from soil or by using towels, clothes or even the comb of infected individuals.
  • Maintenance of personal and public hygiene is very important for prevention and control of many infectious diseases.
  • Measures for personal hygiene include keeping the body clean; consumption of clean drinking water, food, vegetables, fruits, etc.
  • Public hygiene includes proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks and observing standard practices of hygiene in public catering.
  • These measures are essential where the infectious agents are transmitted through food and water such as typhoid, amoebiasis and ascariasis.
  • In cases of air-borne diseases such as pneumonia and common cold, closecontact with the infected persons or their belongings should be avoided.
  • For diseases such as malaria and filariasis the most important measure is to control or eliminate the vectors and their breeding places.
  • This can be achieved by avoiding stagnation of water in and around residential areas, regular cleaning of household coolers, use of mosquito nets, introducing fishes like Gambusia in ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas and swamps, etc.
  • Doors and windows should be provided with wire mesh to prevent the entry of mosquitoes.
  • The use of vaccines and immunisation programmes enables to completely destroy a deadly disease like smallpox.
  • Polio, diphtheria, pneumonia and tetanus have been controlled to a large extent by the use of vaccines. Biotechnology is making available newer and safer vaccines.
  • Discovery of antibiotics and various other drugs has also enabled to effectively treat infectious diseases.


  • The body is able to defend itself from most of the foreign agents.
  • This overall ability of the host to fight the disease-causing organisms, given by the immune system is called immunity.
  • Immunity is of two types: (i) Innate immunity and (ii) Acquired immunity.
  • Innate immunity is non-specific type of defence, that is present at the time of birth.
  • This is accomplished by providing different types of barriers to the entry of the foreign agents into our body. Innate immunity consist of four types of barriers.
  • These are —
  • Physical barriers : Skin on our body is the main barrier which prevents entry of the micro-organisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts also help in trapping microbes entering our body.

(ii) Physiological barriers : Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth.

(iii) Cellular barriers : Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL-neutrophils) and monocytes and natural killer (type of lymphocytes) in the blood as well as macrophages in tissues can phagocytose and destroy microbes.

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(iv) Cytokine barriers : Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.

  • Acquired immunity, on the other hand, is pathogen specific.
  • It is characterised by memory.
  • When our body encounters a pathogen for the first time it produces a response called primary response
  • which is of low intensity.
  • Subsequent encounter with the same pathogen results a highly intensified secondary or anamnestic response.
  • Our body appears to have memory of the first encounter.
  • The primary and secondary immune responses are carried out with the help of two special types of lymphocytes present in our blood, i.e., B-lymphocytes and T lymphocytes.


  • The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies.
  • The T-cells themselves do not secrete antibodies but help B cells produce them.
  • Each antibody molecule has four peptide chains.
  • Two small called light chains and two longer called heavy chains.
  • An antibody is represented as H2L2.


  • Different types of antibodies are produced in our body. IgA, IgM, IgE, IgG are some of them.
  • Because these antibodies are found in the blood, the response is also called as humoral immune response.
  • This is one of the two types of our acquired immune response antibody mediated.
  • The second type is called cell-mediated immune response or cell-mediated immunity (CMI).
  • The T-lymphocytes mediate CMI.
  • The body is able to differentiate ‘self ’ and ‘nonself’ and the cell-mediated immune response is responsible for the graft rejection.


  • When a host is exposed to antigens, antibodies are produced in the host body.
  • This type of immunity is called active immunity.
  • Active immunity is slow and takes time to give its full effective response.
  • When ready-made antibodies are directly given to protect the body against foreign agents, it is called passive immunity.
  • The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant.
  • The foetus also receives some antibodies from their mother, through the placenta during pregnancy.
  • These are some examples of passive immunity.


  • The principle of immunisation or vaccination is based on the property of ‘memory’ of the immune system.
  • In vaccination, a preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) are introduced into the body.
  • The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection.
  • The vaccines also generate memory B and T-cells that recognise the pathogen quickly on subsequent exposure and attack the invaders with a massive production of antibodies.
  • Recombinant DNA technology has allowed the production of antigenic polypeptides of pathogen in bacteria or yeast.
  • Vaccines produced using this approach allow large scale production and hence greater availability for immunisation, e.g., hepatitis B vaccine produced from yeast.



  • The exaggerated response of the immune system to certain antigens present in the environment is called allergy.
  • The substances to which such an immune response is produced are called allergens.
  • The antibodies produced to these are of IgE type. Common examples of allergens are mites in dust, pollens, animal dander, food ,etc.


  • Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing.
  • Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
  • For determining the cause of allergy, the patient is exposed to or injected with very small doses of possible allergens.
  • The use of drugs like anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy. Modern-day life style has resulted in lowering of immunity and more sensitivity to allergens .



  • Memory-based acquired immunity in higher vertebrates has the ability to differentiate foreign organisms (e.g., pathogens) from self cells.
  • Higher vertebrates can distinguish foreign molecules as well as foreign organisms.
  • Sometimes, due to genetic and other unknown reasons, the body attacks self-cells.
  • This results in damage to the body and is called auto-immune
  • Rheumatoid arthritis is an auto-immune disease.



  • The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies.
  • Lymphoid organs: These are the organs where origin and/or maturation and proliferation of lymphocytes occur.
  • The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes.




  • After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.

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  • The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.
  • The bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.
  • The thymus is a lobed organ located near the heart and beneath the breastbone.
  • The thymus is quite large at the time of birth but keeps reducing in size with age and by the time puberty is attained it reduces to a very small size.
  • Both bone-marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes.
  • The spleen is a large beanshaped organ.
  • It mainly contains lymphocytes and phagocytes.
  • It acts as a filter of the blood by trapping blood-borne micro organisms.
  • Spleen also has a large reservoir of erythrocytes.
  • The lymph nodes are small solid structures located at different points along the lymphatic system.
  • Lymph nodes serve to trap the micro-organisms or other antigens.
  • Antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.
  • There is lymphoid tissue also located within the lining of the major tracts (respiratory, digestive and urogenital tracts) called mucosal associated lymphoid tissue (MALT).
  • It constitutes about 50 per cent of the lymphoid tissue in human body.


  • Acquired Immuno Deficiency Syndrome.
  • Deficiency of immune system, acquired during the lifetime of an individual.
  • It is not a congenital disease.
  • Syndrome means a group of symptoms.
  • AIDS was first reported in 1981.
  • AIDS is caused by the Human Immuno deficiency Virus(HIV).


  • A member of a group of viruses called
  • Have an envelope enclosing the RNA genome.
  • Transmission of HIV-infection occurs by
  1. sexual contact with infected person,
  2. by transfusion of contaminated blood and blood products
  • by sharing infected needles as in the case of intravenous drug abusers from infected mother to her child through placenta.
  • People at high risk of getting this infection includes individuals who have multiple sexual partners, drug addicts who take drugs intravenously, individuals who require repeated blood transfusions and children born to an HIV infected mother.
  • HIV/AIDS is not spread by mere touch or physical contact.
  • It spreads only through body fluids.
  • There is always a time-lag between the infection and appearance of AIDS symptoms.
  • This period may vary from a few months to many years (usually 5-10 years).
  • After getting into the body of the person, the virus enters into macrophages where RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase.
  • This viral DNA gets incorporated into host cell’s DNA and directs the infected cells to produce virus particles
  • The macrophages continue to produce virus and in this way acts like a HIV factory.
  • HIV enters into helper T-lymphocytes (TH), replicates and produce progeny viruses.
  • The progeny viruses released in the blood attack other helper T-lymphocytes.
  • This is repeated leading to a decrease in the number of helper T-lymphocytes.
  • During this period, the person suffers from fever, diarrhoea and weight loss.
  • Due to decrease in the number of helper T lymphocytes, the person starts suffering from infections.
  • The patient becomes so immuno-deficient that he/she is unable to protect himself/herself against these infections.
  • A widely used diagnostic test for AIDS is enzyme linked immuno-sorbent assay (ELISA).
  • Treatment of AIDS with anti-retroviral drugs is only partially effective.
  • They can only prolong the life of the patient but cannot prevent death.
  • As AIDS has no cure, prevention is the best option.
  • In our country the National AIDS Control Organisation (NACO) and other non-governmental organisation (NGOs) are doing a lot to educate people about AIDS. WHO has started a number of programmes to prevent the spreading of HIV infection.
  • Steps taken to prevent HIV infection :
  1. Making blood (from blood banks) safe from
  2. HIV
  • Use of only disposable needles and syringes in public and private hospitals and clinics.
  1. Free distribution of condoms.
  2. Controlling drug abuse.
  3. Advocating safe sex.
  • Promoting regular check-ups for HIV in susceptible populations.


  • Cancer is one of the most dreaded diseases of human beings.
  • Major cause of death all over the globe.
  • In our body, cell growth and differentiation is highly controlled and regulated.
  • In cancer cells, there is breakdown of these regulatory mechanisms.
  • Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth.
  • Cancer cells appears to have lost this property.
  • As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.
  • Tumors are of two types: benign and malignant.


  • Benign tumors normally remain confined to their original location and do not spread to other parts of the body and cause little damage.
  • The malignant tumors, on the other hand are a mass of proliferating cells called neoplastic or tumor cells.
  • These cells grow very rapidly, invading and damaging the surrounding normal tissues.
  • They also starve the normal cells by competing for vital nutrients.
  • Cells sloughed from such tumors reach distant sites through blood, and wherever they get lodged in the body, they start a new tumor there.
  • This property called metastasis is the most feared property of malignant tumors.
  • Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents.
  • These agents are called carcinogens.
  • Ionising radiations like X-rays and gamma rays and non-ionizing radiations like UV cause DNA damage leading to neoplastic transformation.
  • The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.
  • Cancer causing viruses called oncogenic viruses have genes called viral oncogenes.
  • Several genes called cellular oncogenes (c-onc) or proto oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic transformation of the cells.
  • Early detection of cancers is essential
  • Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias.
  • In biopsy, a piece of the suspected tissue cut into thin sections is stained and examined under microscope Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs.
  • Computed tomography uses X-rays to generate a three-dimensional image of the internals of an object. MRI uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in the living tissue.
  • Antibodies against cancer-specific antigens are also used for detection of certain cancers.
  • Techniques of molecular biology can be applied to detect genes in individuals with inherited susceptibility to certain cancers.
  • Identification of such genes may be very helpful in prevention of cancers.
  • Such individuals may be advised to avoid exposure to particular carcinogens to which they are susceptible.
  • The common approaches for treatment of cancer are surgery, radiation therapy and immunotherapy.
  • In radiotherapy, tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass.
  • Several chemotherapeutic drugs are used to kill cancerous cells.
  • Majority of drugs have side effects like hair loss, anemia, etc.
  • Most cancers are treated by combination of surgery, radiotherapy and chemotherapy.
  • Tumor cells have been shown to avoid detection and destruction by immune system.
  • Therefore, the patients are given substances called biological response modifiers such as ã-interferon which activate their immune system and help in destroying the tumor.


  • The drugs, which are commonly abused are opioids, cannabinoids and coca alkaloids.
  • Majority of these are obtained from flowering plants.
  • Some are obtained from fungi.
  • Opioids are the drugs, which bind to specific opioid receptors present in our central nervous system and gastrointestinal tract.
  • Heroin commonly called smack is chemically diacetylmorphine which is a white, odourless, bitter crystalline compound.
  • This is obtained by acetylation of morphine which is extracted from the latex of poppy plant Papaver somniferum.


  • Generally taken by snorting and injection.
  • Heroin is a depressant and slows down body functions.
  • Cannabinoids are a group of chemicals which interact with cannabinoid receptors present in the brain.
  • Natural cannabinoids are obtained from the inflorescences of the plant Cannabis sativa .


  • The flower tops, leaves and the resin of cannabis plant are used in various combinations to produce marijuana, hashish, charas and ganja.
  • Generally taken by inhalation and oral ingestion
  • They effect on cardiovascular system of the body.
  • Coca alkaloid or cocaine is obtained from coca plant Erythroxylum coca, native to South America.


  • It interferes with the transport of the neuro-transmitter dopamine.
  • Usually snorted.
  • It has a potent stimulating action on central nervous system, producing a sense of euphoria and increased energy.
  • Excessive dosage of cocaine causes hallucinations.
  • Other well-known plants with hallucinogenic properties are Atropa belladona and Datura.
  • Cannabinoids are also being abused by some sportspersons.
  • Drugs like barbiturates, amphetamines, benzodiazepines, lysergic acid diethyl amides (LSD), and other similar drugs, that are normally used as medicines to help patients cope with mental illnesses like depression and insomnia.
  • Morphine is a very effective sedative and painkiller, Useful in patients who have undergone surgery.
  • It impairs one’s physical, physiological or psychological functions.
  • Tobacco has been used by human beings for more than 400 years.
  • It is smoked, chewed or used as a snuff.
  • Tobacco contains a large number of chemical substances including nicotine, an alkaloid.
  • Nicotine stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation.
  • Raise blood pressure and increase heart rate.
  • Smoking is associated with increased incidence of cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer, etc. Tobacco chewing is associated with increased risk of cancer of the oral cavity.
  • Smoking increases carbon monoxide (CO) content in blood and reduces the concentration of haembound oxygen.
  • This causes oxygen deficiency in the body.


  • Adolescence means both ‘a period’ and ‘a process’ during which a child becomes mature in terms of his/her attitudes and beliefs for effective participation in society. The period between 12-18 years of age may be thought of as adolescence period.
  • Adolescence is a bridge linking childhood and adulthood. Adolescence is accompanied by several biological and behavioural changes.
  • Very vulnerable phase of mental and psychological development of an individual.
  • The first use of drugs or alcohol may be out of curiosity or experimentation.
  • Television, movies, newpapers, internet also help to promote this perception.
  • Other factors that have been seen to be associated with drug and alcohol abuse among adolescents are unstable or unsupportive family structures and peer pressure.



  • Addiction is a psychological attachment to certain effects.
  • Such as euphoria and a temporary feeling of well-being associated with drugs and alcohol.
  • These drive people to take them even when these are not needed, or even when their use becomes self-destructive.
  • With repeated use of drugs, the tolerance level of the receptors present in our body increases.
  • Consequently the receptors respond only to higher doses of drugs or alcohol leading to greater intake and addiction.
  • This is characterised by anxiety, shakiness, nausea and sweating, which may be relieved when use is resumed again.
  • In some cases, withdrawal symptoms can be severe and even life threatening and the person may need medical supervision.
  • Dependence leads the patient to ignore all social norms These result in many social adjustment problems.


  • Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral hemorrhage.
  • A combination of drugs or their intake along with alcohol generally results in overdosing and even deaths.
  • The adverse effects are just not restricted to the person who is using drugs or alcohol.
  • At times, a drug/alcohol addict becomes the cause of mental and financial distress to his/her entire family and friends.
  • Those who take drugs intravenously (direct injection into the vein using a needle and syringe), are much more likely to acquire serious infections like AIDS and hepatitis B.
  • The use of alcohol during adolescence may also have long-term effects.
  • It could lead to heavy drinking in adulthood.
  • The chronic use of drugs and alcohol damages nervous system and liver (cirrhosis).
  • The use of drugs and alcohol during pregnancy is also known to adversely affect the foetus.
  • Another misuse of drugs is sportspersons do to enhance their performance.
  • They (mis)use narcotic analgesics, anabolic steroids, diuretics and certain hormones in sports.
  • To increase muscle strength and bulk to increase athletic performance.
  • The side-effects of the use of anabolic steroids in females include masculinisation (features like males), increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive hair growth on the face and body, enlargement of clitoris, deepening of voice.
  • In males it includes acne, increased aggressiveness, mood swings, depression, reduction of size of the testicles, decreased sperm production, potential for kidney and liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland. These effects may be permanent with prolonged use.


  • Parenting that combines with high levels of nurturance
  • and consistent discipline, has been associated with lowered risk of substance (alcohol/drugs/tobacco) abuse.
  • Some of the measures to prevent and control the abuse :
  • Avoid undue peer pressure
  • Education and counselling
  • Seeking help from parents and peers
  • Looking for danger signs
  • Seeking professional and medical help