Some of the most noticeable symptoms of drug abuse are those that affect the body’s inner workings. For example, your body’s tolerance to a drug occurs when a drug is abused for long enough that increased quantities or strengths are required to achieve the previous effects. This desire for a more intense high, achieved through these means, is extremely dangerous and can easily lead to overdose.

The diminishing effects set in after the first time, and the user constantly tries to replicate the first high he or she gets from the drug by taking increasing amounts. This is extremely dangerous and can quickly lead to overdose.

Changes in appearance can be additional clues to possible drug use and may include:

Bloodshot or glazed eyes.
Dilated or constricted pupils.
Abrupt weight changes.
Bruises, infections, or other physical signs at the drug’s entrance site on the body.
Disruption to normal brain functioning, changes in personality, and heart and organ dysfunction can be signs of long-term drug abuse. Signs will vary based on the substance. Click on any drug above to learn more.

Behavioral Symptoms
Drug abuse negatively affects a person's behavior and habits as he or she becomes more dependent on the drug. The drug itself can alter the brain's ability to focus and form coherent thoughts, depending on the substance.

Changes in behavior, such as the following, can indicate a problem with drug abuse:

Increased aggression or irritability.
Changes in attitude/personality.
Sudden changes in a social network.
Dramatic changes in habits and/or priorities.
Financial problems.
Involvement in criminal activity.
Learning to recognize the physical or behavioral signs of drug abuse can help prevent the problem from progressing further.