Drug addiction symptoms or behaviors include, among others: 
Feeling that you have to use the drug regularly — daily or even several times a day
Having intense urges for the drug that block out any other thoughts
Over time, needing more of the drug to get the same effect
Taking larger amounts of the drug over a longer period of time than you intended
Making certain that you maintain a supply of the drug
Spending money on the drug, even though you can't afford it
Not meeting obligations and work responsibilities, or cutting back on social or recreational activities because of drug use
Continuing to use the drug, even though you know it's causing problems in your life or causing you physical or psychological harm
Doing things to get the drug that you normally wouldn't do, such as stealing
Driving or doing other risky activities when you're under the influence of the drug
Spending a good deal of time getting the drug, using the drug or recovering from the effects of the drug
Failing in your attempts to stop using the drug
Experiencing withdrawal symptoms when you attempt to stop taking the drug
 Recognizing unhealthy drug use in family members Sometimes it's difficult to distinguish normal teenage moodiness or anxiety from signs of drug use. Possible signs that your teenager or other family member is using drugs include: 
Problems at school or work — frequently missing school or work, a sudden disinterest in school activities or work, or a drop in grades or work performance
Physical health issues — lack of energy and motivation, weight loss or gain, or red eyes
Neglected appearance — lack of interest in clothing, grooming or looks
Changes in behavior — major efforts to bar family members from entering the teenager's room or being secretive about going out with friends; or drastic changes in behavior and in relationships with family and friends
Money issues — sudden requests for money without a reasonable explanation; or your discovery that money is missing or has been stolen or that items have disappeared from your home, indicating maybe they're being sold to support drug use
 Recognizing signs of drug use or intoxication Signs and symptoms of drug use or intoxication may vary, depending on the type of drug. Below you'll find several examples. Marijuana, hashish and other cannabis-containing substances People use cannabis by smoking, eating or inhaling a vaporized form of the drug. Cannabis often precedes or is used along with other substances, such as alcohol or illegal drugs, and is often the first drug tried. Signs and symptoms of recent use can include: 
A sense of euphoria or feeling "high"
A heightened sense of visual, auditory and taste perception
Increased blood pressure and heart rate
Red eyes
Dry mouth
Decreased coordination
Difficulty concentrating or remembering
Slowed reaction time
Anxiety or paranoid thinking
Cannabis odor on clothes or yellow fingertips
Major cravings for certain foods at unusual times
 Long-term use is often associated with: 
Decreased mental sharpness
Poor performance at school or at work
Ongoing cough and frequent lung infections
 K2, Spice and bath salts Two groups of synthetic drugs — synthetic cannabinoids and substituted or synthetic cathinones — are illegal in most states. The effects of these drugs can be dangerous and unpredictable, as there is no quality control and some ingredients may not be known. Synthetic cannabinoids, also called K2 or Spice, are sprayed on dried herbs and then smoked, but can be prepared as an herbal tea. A liquid form can be vaporized in electronic cigarettes. Despite manufacturer claims, these are chemical compounds rather than "natural" or harmless products. These drugs can produce a "high" similar to marijuana and have become a popular but dangerous alternative. Signs and symptoms of recent use can include: 
A sense of euphoria or feeling "high"
Elevated mood
An altered sense of visual, auditory and taste perception
Extreme anxiety or agitation
Paranoia
Hallucinations
Increased heart rate and blood pressure or heart attack
Vomiting
Confusion
Violent behavior
 Substituted cathinones, also called "bath salts," are mind-altering (psychoactive) substances similar to amphetamines such as ecstasy (MDMA) and cocaine. Packages are often labeled as other products to avoid detection. Despite the name, these are not bath products such as Epsom salts. Substituted cathinones can be eaten, snorted, inhaled or injected and are highly addictive. These drugs can cause severe intoxication, which results in dangerous health effects or even death. Signs and symptoms of recent use can include: 
Feeling "high"
Increased sociability
Increased energy and agitation
Increased sex drive
Increased heart rate and blood pressure
Problems thinking clearly
Loss of muscle control
Paranoia
Panic attacks
Hallucinations
Delirium
Psychotic and violent behavior
 Barbiturates, benzodiazepines and hypnotics Barbiturates, benzodiazepines and hypnotics are prescription central nervous system depressants. They're often used and misused in search for a sense of relaxation or a desire to "switch off" or forget stress-related thoughts or feelings. 
Barbiturates. An example is phenobarbital.
Benzodiazepines. Examples include sedatives, such as diazepam (Valium), alprazolam (Xanax), lorazepam (Ativan), clonazepam (Klonopin) and chlordiazepoxide (Librium).
Hypnotics. Examples include prescription sleeping medicines such as zolpidem (Ambien) and zaleplon (Sonata).
 Signs and symptoms of recent use can include: 
Drowsiness
Slurred speech
Lack of coordination
Irritability or changes in mood
Problems concentrating or thinking clearly
Memory problems
Involuntary eye movements
Lack of inhibition
Slowed breathing and reduced blood pressure
Falls or accidents
Dizziness
 Meth, cocaine and other stimulants Stimulants include amphetamines, meth (methamphetamine), cocaine, methylphenidate (Ritalin, Concerta, others) and amphetamine-dextroamphetamine (Adderall XR, Mydayis). They're often used and misused in search of a "high," or to boost energy, to improve performance at work or school, or to lose weight or control appetite. Signs and symptoms of recent use can include: 
Feeling of happy excitement and too much confidence
Increased alertness
Increased energy and restlessness
Behavior changes or aggression
Rapid or rambling speech
Larger than usual pupils, the black circles in the middle of the eyes
Confusion, delusions and hallucinations
Irritability, anxiety or paranoia
Changes in heart rate, blood pressure and body temperature
Nausea or vomiting with weight loss
Poor judgment
Nasal congestion and damage to the mucous membrane of the nose (if snorting drugs)
Mouth sores, gum disease and tooth decay from smoking drugs ("meth mouth")
Insomnia
Depression as the drug wears off
 Club drugs Club drugs are commonly used at clubs, concerts and parties. Examples include methylenedioxymethamphetamine, also called MDMA, ecstasy or molly, and gamma-hydroxybutyric acid, known as GHB. Other examples include ketamine and flunitrazepam or Rohypnol ― a brand used outside the U.S. ― also called roofie. These drugs are not all in the same category, but they share some similar effects and dangers, including long-term harmful effects. Because GHB and flunitrazepam can cause sedation, muscle relaxation, confusion and memory loss, the potential for sexual misconduct or sexual assault is associated with the use of these drugs. GHB Signs and symptoms of use of club drugs can include: 
Hallucinations
Paranoia
Larger than usual pupils
Chills and sweating
Involuntary shaking (tremors)
Behavior changes
Muscle cramping and teeth clenching
Muscle relaxation, poor coordination or problems moving
Reduced inhibitions
Heightened or altered sense of sight, sound and taste
Poor judgment
Memory problems or loss of memory
Reduced consciousness
Increased or decreased heart rate and blood pressure
 Hallucinogens Use of hallucinogens can produce different signs and symptoms, depending on the drug. The most common hallucinogens are lysergic acid diethylamide (LSD) and phencyclidine (PCP). LSD use may cause: LSD 
Hallucinations
Greatly reduced perception of reality, for example, interpreting input from one of your senses as another, such as hearing colors
Impulsive behavior
Rapid shifts in emotions
Permanent mental changes in perception
Rapid heart rate and high blood pressure
Tremors
Flashbacks, a reexperience of the hallucinations — even years later
 PCP use may cause: PCP 
A feeling of being separated from your body and surroundings
Hallucinations
Problems with coordination and movement
Aggressive, possibly violent behavior
Involuntary eye movements
Lack of pain sensation
Increase in blood pressure and heart rate
Problems with thinking and memory
Problems speaking
Poor judgment
Intolerance to loud noise
Sometimes seizures or coma
 Inhalants Signs and symptoms of inhalant use vary, depending on the substance. Some commonly inhaled substances include glue, paint thinners, correction fluid, felt tip marker fluid, gasoline, cleaning fluids and household aerosol products. Due to the toxic nature of these substances, users may develop brain damage or sudden death. Signs and symptoms of use can include: 
Possessing an inhalant substance without a reasonable explanation
Brief happy excitement
Behaving as if drunk
Reduced ability to keep impulses under control
Aggressive behavior or eagerness to fight
Dizziness
Nausea or vomiting
Involuntary eye movements
Appearing under the influence of drugs, with slurred speech, slow movements and poor coordination
Irregular heartbeats
Tremors
Lingering odor of inhalant material
Rash around the nose and mouth
 Opioid painkillers Opioids are narcotic, painkilling drugs produced from opium or made synthetically. This class of drugs includes, among others, heroin, morphine, codeine, methadone, fentanyl and oxycodone. Sometimes called the "opioid epidemic," addiction to opioid prescription pain medicines has reached an alarming rate across the United States. Some people who've been using opioids over a long period of time may need physician-prescribed temporary or long-term drug substitution during treatment. Signs and symptoms of narcotic use and dependence can include: 
A sense of feeling "high"
Reduced sense of pain
Agitation, drowsiness or sedation
Slurred speech
Problems with attention and memory
Pupils that are smaller than usual
Lack of awareness or inattention to surrounding people and things
Problems with coordination
Depression
Confusion
Constipation
Runny nose or nose sores (if snorting drugs)
Needle marks (if injecting drugs)
