Cannabis

Cannabis is a drug that comes from Indian hemp plants such as Cannabis sativa and Cannabis indica. The active chemical in cannabis is THC (Delta-9 tetrahydrocannabinol).
 
Cannabis is a depressant drug. Depressants affect the central nervous system by slowing down the messages going between the brain and the body. THC ((Delta-9 tetrahydrocannabinol) is the chemical that makes you feel “high”. This means you experience a change in mood and may see or feel things in different ways than usual.

What does it look like?

There are three main forms of cannabis:

• Marijuana is the most common and least powerful form of cannabis. It is the dried leaves and flowers of the plant. Marijuana looks like chopped grass, and ranges in color from grey-green to greenish-brown. Marijuana is smoked in hand-rolled cigarettes (joints) or in a pipe (a bong).
• Hashish (hash) is dried cannabis resin which comes in small blocks. The blocks range in color from light brown to nearly black. The concentration of THC in hashish is higher than in marijuana, producing stronger effects. Hash is added to tobacco and smoked, or baked and eaten in foods such as "hash cookies".
• Hash oil is a thick, oily liquid, golden-brown to black, that can be extracted from hashish. It is usually spread on the tip or paper of cigarettes and then smoked. Hash oil is more powerful than the other forms of cannabis. This form is rarely found in Australia.

THC

THC (delta-9 tetrahydrocannabinol) is the chemical in cannabis that makes you feel "high". This means you experience a change in mood and may see or feel things in a different way. Some parts of the plant contain a higher level of THC. For example, the flowers, or "heads", have more THC than the stems and leaves.

THC is absorbed into the bloodstream through the walls of the lungs (if cannabis is smoked), or through the walls of the stomach and intestines (if eaten). The bloodstream carries the THC to the brain, producing the "high" effects. Drugs that are inhaled get into the bloodstream quicker than those eaten.

Immediate effects

Small doses of cannabis can have effects that last 2–4 hours after smoking. These effects include:

• relaxation and loss of inhibition
• increased appetite
• affected perception of color, sound and other sensations
• impaired coordination
• affected thinking and memory.

Other common immediate effects include increased heart rate, low blood pressure and reddened eyes.

In greater quantities

Larger quantities of marijuana make the above effects stronger, and also tend to distort a person’s perceptions.
Very large quantities of marijuana produce:

• confusion
• restlessness
• hallucinations
• anxiety or panic, or detachment from reality
• decreased reaction time
• paranoia

Long-term effects

Research shows evidence of long-term effects in some regular cannabis users. 

• Respiratory illness
  Marijuana cigarettes have more tar than tobacco, placing cannabis users at an increased risk of respiratory illness such as lung cancer and chronic bronchitis. Cigarette smokers who also smoke cannabis have an even greater risk of respiratory disease.
• Reduced motivation
  Many regular users have reported that they have less energy and motivation, so that performance at work or school suffers.
• Brain function
  Concentration, memory and the ability to learn can all be reduced by regular cannabis use. These effects can last for several months after ceasing cannabis use.
• Hormones 
  Cannabis can affect hormone production. Research shows that some cannabis users have a lower sex drive. Irregular menstrual cycles and lowered sperm counts have also been reported.
• Immune system
  There is some concern that cannabis smoking may impair the functioning of the immune system.

Cannabis and Psychosis

It is believed that cannabis use—especially if heavy and regular—may be linked to a condition known as a drug-induced psychosis, or "cannabis psychosis". This can last up to a few days. The episodes are often characterized by hallucinations, delusions, memory loss and confusion.

There is some evidence that regular cannabis use increases the likelihood of psychotic symptoms occurring in an individual who is vulnerable due to a personal or family history of mental illness. Cannabis also appears to make psychotic symptoms worse for those with schizophrenia and lowers the chances of recovery from a psychotic episode.

Tolerance and dependence

With regular use, people can develop a mild tolerance to cannabis. This means they need to take more and more to get the same effect.
Heavy and frequent use of cannabis can cause physical dependence. Physical dependence occurs when a person’s body has adapted to a drug and is used to functioning with the drug present.

It is possible to become psychologically dependent on cannabis. This means that using cannabis becomes far more important than other activities in their life. Some people crave the drug and find it very difficult to stop using it.

Withdrawal

Abrupt termination of cannabis use can produce withdrawal symptoms. Withdrawal symptoms include sleep disturbance, irritability, loss of appetite, nervousness, anxiety, sweating and upset stomach. Sometimes chills, increased body temperature and tremors occur. The withdrawal symptoms usually last for less than a week, although the sleep disturbances may persist for longer.

• For more information on the risks of cannabis-related harm, contact the alcohol and drug information service in your state or territory.