When we talk about drug addiction we have to make a clear separation between physiological and psychological addiction.
We talk about physiological addiction when the body protests due to the stopping of the drug. Withdrawal symptoms arise. Another physical aspect of drug addiction is tolerance. This means that the user needs to increase the intake substance to get the same effect. Physical dependence and tolerance are caused by the drug itself. There are drugs that cause both phenomena, but there are those that do not arise either one of them.

Psychological dependence means that the user has the idea that he or she can not function without the use of more drugs. Psychological dependence comes more from the user, rather than the substance itself.
The first sign is irresistible attraction to a substance or the so called psychological dependence /need/. Demand is a major symptom of the disease. It can be periodical or constant. The motives behind it are different. Most often there is the desire of the addicted to free himself from the state of inner tension and depression, to eliminate the poor self-confidence or to achieve euphoria, to better his social contacts, mood and work performance.

The second sign is the change of tolerance to a substance. In all drug abuses tolerance of the organism to the substance continuously increases over time. To some extent an exception is the alcohol dependency /alcoholic disease/ where tolerance is first increases and then decreases and the patient is drunk from smaller amounts of alcohol. The increased tolerance is one of the early signs of the disease. On the other hand tolerance to one drug can pass in tolerance to other similar chemically or pharmacological substances.

The third main indicator for abstinence when the substance use has stopped is the psychological and psychical discomfort – a feeling of anxiety and fear, irritability, mood swings, fast heart beat, sweating and pain in the body.
Other common signs of Toxicomania are loss of control over the intake of the substance and enduring constant physical and mental disorders.
There are addictions to several groups of substances:

Opiates such as:
Heroin, morphine and methadone etc
Benzodiazepines – lexotane, diazepame, relanium, tranksen, Xanax and others
Cocaine, ecstasy, amphetamine, methamphetamine, piko and others
Alcohol – rakia, vodka, whiskey, gin, wine, beer etc.
hallucinogenic agents
LSD, hallucinogenic mushrooms, barbiturates etc.
cannabis (marijuana, hashish)