15.3) Misused drugs

15.3) Misused drugs


Effects of excessive alcohol consumption and abuse of heroin:

  • Powerful depressant drugs
  • Effect on reaction times and self-control
  • Addiction and withdrawal symptoms
  • Negative social implications, eg. crime


How heroin affects the nervous system:

  • Produces it effects by interacting with receptor molecules at synapse.
  • Heroin mimics the transmitter substances in synapses in the brain, causing the release of dopamine (a neurotransmitter), which gives a short lived ‘high’.


  • Injecting heroin can cause infections such as HIV.
  • Excessive alcohol consumption can cause liver damage.
  • Tobacco smoking can cause chronic obstructive pulmonary disease (COPD), lung cancer and coronary heart disease.
  • Liver is the site of breakdown of alcohol and other toxins.


Evidence for a link between smoking and lung cancer:

There are at least 17 substances in tobacco smoke known to cause cancer in experimental animals, and it is now thought that 90% of lung cancer is caused by smoking.


  • Nicotine, the addictive component of tobacco smoke, produces an increase in the rate if the heartbeat and a rise in blood pressure and can cause an erratic and irregular heart beat.
  • Tar in cigarette smoke is thought to be the main cause of lung cancer in smokers.
  • Carbon monoxide permanently binds with haemoglobin in red blood cells, reducing the smoker’s ability to provide oxygen to respiring cells. This results in a smoker getting out of breath more easily and it reduces physical fitness.


The nicotine and carbon monoxide increase the tendency for the blood to clot and so block the coronary arteries.


Performance-enhancing hormones:


  • Is made in the testes of males and is responsible for promoting male primary and secondary sexual characteristics.
  • Taking testosterone supplements (known as ‘doping’) leads to increased muscle and bone mass.
  • Which can enhance a sports person’s performance.

Anabolic steroids

  • Are synthetic derivatives of testosterone.
  • They affect protein metabolism, increasing muscle development and reducing body fat.
  • Athletic performance is thus enhanced.
  • There are serious long-term effects of taking anabolic steroids: sterility, masculinisation in women, and liver and kidney malfunction.