1. By jonty

2. Drugs generally work by interacting with receptors on the surface of cells or enzymes (which regulate the rate of chemical reactions) within cells. Most drugs work because by binding to the target receptor site, they can either block the physiological function of the protein, or mimics it's effect. If a drug causes the protein receptor to respond in the same way as the naturally occurring substance, then the drug is referred to as an agonist. Examples of agonists are morphine, nicotine, phenylephrine, and isoproterenol. Antagonists are drugs that interact selectively with receptors but do not lead to an observed effect.

3. e.g Anabolic steroids Anabolic steroids increase the rate of protein synthesis within cells. The building of cellular tissue (anabolism) is especially noticeable in muscles. Anabolic steroids change muscle mass and strength by two processes. First, the steroids lead to an increased production of proteins, which are the building blocks of muscle. The steroids also block the effect of the hormone cortisol on muscle tissue, so that existing muscle is broken down at a slower rate. Additionally, anabolic steroids lead to cells differentiating into muscle more readily than fat.

4. There are lots of illegal drugs e.g Cocaine and crack cocaine come from the leaves of the coca plant which grows primarily in South America. Cocaine is processed into a white powder which people snort or melt and inject. Crack is further processed into a substance that can be smoked. Cocaine is a Schedule II controlled substance. It is illegal to grow, process, sell or use cocaine or crack. Cocaine has limited use in medicine as an anaesthetic. And Opium is the dried milk of the poppy plant and contains morphine and codeine from morphine it is a short step to the production of heroin, a powder over twice as potent as morphine. Opium can be eaten, smoked and drunk. Morphine can be injected or taken orally. Heroin can be smoked in tobacco, heated on aluminium foil and inhaled, injected under the skin or into the muscle/ vein.