Cocaine is found in several species of plants, most notably erythroxylon coca, which predominantly grows in the Andes region of South America. Medicinally, it has been used as an anesthetic. However, its medicinal form is rarely found "on the street" and it is also rarely used in modern medical procedures. The two most common forms of cocaine are white powder or freebase cocaine (that is often snorted or injected) and "crack" cocaine, a solid chunk of cocaine that is heated and creates a vapor that is inhaled.
Cocaine works by increasing the amount of monoamine neurotransmitters (norepinephrine, epinephrine, serotonin, & dopamine) in the synapses between nerve cells in the brain. More specifically, it is the excess dopamine that increases reinforcement or "reward," a feeling of pleasure, that is linked to cocaine's addictive potential.
Small amounts of cocaine can lead to a user feeling energetic, euphoric, talkative, alert, and hypersensitive to sensory experiences. Physiological effects include constricted blood vessels, increased body temperature, heart rate, and blood pressure. When cocaine is used in large amounts, it can lead to harmful effects including anxiety/panic, paranoia, tremors, heart attack, seizures, and stroke.
Because cocaine is metabolized so quickly, the initial euphoria, feeling of confidence, sense of omnipotence, surge of energy, and sense of satisfaction disappear as suddenly as they appeared, resulting in a crash after use that can be intensely depressing; this depression can last a few hours, several days, or even weeks.
The short answer is: yes. Repeat cocaine use alters the reward pathways in the brain, making users less sensitive to natural reinforcers such as relationships, food, and sleep. At the same time, stress circuits in the brain become more sensitive, which can lead to negative mood states when not using the drug, known as psychological withdrawal. These two variables contribute to drug-seeking behavior in users and increase the potential that users will become dependent.