Substance Use Disorders
Substance use disorders (SUDs) describe a pattern where someone continues using a substance despite significant harm to their health, relationships, or daily functioning. The DSM-5 organizes the diagnostic criteria into four clusters: impaired control, social impairment, risky use, and pharmacological effects. A person doesn't need to meet all of them, but the more criteria they meet, the more severe the disorder is classified (mild, moderate, or severe).
Criteria for Substance Use Disorders
Impaired control
- Using more than intended: Taking larger amounts or using for longer than planned, often driven by tolerance or compulsive patterns (e.g., planning to have two drinks but finishing the bottle)
- Unsuccessful efforts to quit: Repeatedly trying to cut down or stop but being unable to maintain it (e.g., failed attempts to quit smoking, relapsing after a period of sobriety)
- Excessive time spent on the substance: Obtaining, using, or recovering from the substance takes up so much time that responsibilities get neglected (e.g., spending entire weekends hungover, skipping work to obtain drugs)
- Cravings: Strong urges to use, often triggered by environmental cues or the onset of withdrawal (e.g., craving nicotine when stressed, feeling a pull to use when passing a familiar location)
Social impairment
- Failing to meet obligations: Performance at work, school, or home suffers because of substance use (e.g., missing deadlines, neglecting childcare)
- Continued use despite relationship problems: Keeping up use even when it causes or worsens conflicts with others (e.g., arguments with a partner about drinking, losing friendships)
- Withdrawal from activities: Dropping hobbies, social events, or other meaningful activities in favor of substance use (e.g., quitting a sports team, isolating from family)
Risky use
- Use in dangerous situations: Repeatedly using in contexts where it's physically hazardous (e.g., driving under the influence, operating heavy machinery while impaired)
- Use despite known harm: Continuing even with awareness that the substance is causing or worsening a physical or psychological problem (e.g., drinking despite liver disease, smoking despite a lung condition)
Pharmacological criteria
- Tolerance: The brain adapts to the substance over time, so you need more of it to get the same effect, or the same dose produces a weaker effect. This is why someone who drinks regularly can "handle more" than someone who rarely drinks.
- Withdrawal: When the substance leaves the body, uncomfortable or even dangerous symptoms appear. Examples include tremors and nausea when an alcohol-dependent person stops drinking, or flu-like symptoms when someone dependent on opioids goes without them. People sometimes keep using just to avoid these withdrawal effects.
Drug Interactions with Neurotransmitters
Each drug category affects the brain differently by targeting specific neurotransmitter systems. Understanding these mechanisms helps explain why different substances produce such different experiences.
Stimulants (cocaine, amphetamines)
- Boost dopamine levels in the brain's reward pathway, producing euphoria and reinforcing repeated use. Cocaine blocks dopamine reuptake, while amphetamines push extra dopamine into the synapse.
- Also increase norepinephrine and serotonin activity, which elevates heart rate, sharpens focus, and affects mood.
Depressants (alcohol, benzodiazepines, barbiturates)
- Enhance the effects of GABA, the brain's main inhibitory neurotransmitter, producing sedation and reducing anxiety.
- Suppress glutamate, the main excitatory neurotransmitter, which impairs memory formation and coordination. This is why alcohol can cause blackouts and poor motor control.
Opioids (heroin, morphine, prescription painkillers like oxycodone)
- Bind to mu-opioid receptors, which are involved in pain relief and reward. This is why opioids are so effective at blocking pain but also so addictive.
- Trigger dopamine release in the reward pathway, producing intense euphoria (the "rush" associated with heroin use).
Hallucinogens (LSD, psilocybin)
- Act primarily on serotonin 5-HT2A receptors, which are involved in perception and cognition. This produces visual distortions, altered thinking, and changes in the sense of self.
- Also alter glutamate transmission in the prefrontal cortex, which can affect mood, insight, and feelings of connectedness.
Cannabinoids (marijuana/THC)
- Activate cannabinoid receptors (CB1 and CB2). CB1 receptors are concentrated in brain areas involved in appetite, pain sensation, and memory, which explains effects like increased hunger and pain relief.
- Modulate the release of multiple neurotransmitters, including dopamine, GABA, and glutamate, producing the characteristic "high" along with impaired short-term memory.
Effects of Drug Categories
Stimulants
- Increased alertness, energy, and confidence from norepinephrine and dopamine release
- Decreased appetite and disrupted sleep due to elevated arousal (can lead to significant weight loss and insomnia with chronic use)
- At high doses, excessive dopamine can cause anxiety, paranoia, and even stimulant-induced psychosis
Depressants
- Sedation, relaxation, and reduced anxiety from enhanced GABA activity
- Impaired coordination, judgment, and memory (slurred speech, poor decision-making)
- At high doses, depressants can suppress brainstem function enough to cause respiratory depression, coma, or death. This risk increases sharply when depressants are combined (e.g., mixing alcohol with benzodiazepines).
Opioids
- Powerful pain relief, euphoria, and sedation from mu-opioid receptor activation
- Slowed breathing, constipation, and itching as side effects across respiratory, digestive, and sensory systems
- Very high potential for dependence and fatal overdose. Tolerance builds quickly, pushing users toward higher doses, while the margin between an effective dose and a lethal dose narrows.
Hallucinogens
- Altered perceptions, thoughts, and emotions (seeing vivid colors and patterns, feeling profound insights)
- Heightened sensory experiences and feelings of detachment from the self
- Potential for intensely negative emotional reactions ("bad trips") and impaired judgment. Unlike most other drug categories, hallucinogens generally carry low risk of physical dependence.
Cannabinoids
- Relaxation, altered time perception, and increased appetite from CB1 receptor activation
- Impaired short-term memory, learning, and coordination due to effects on the hippocampus and cerebellum
- In some individuals, cannabis can trigger anxiety, paranoia, or, in rare cases, psychosis. Vulnerability varies based on genetics and individual differences in the endocannabinoid system.
Addiction and Treatment
These terms come up frequently and are worth knowing precisely:
- Addiction is a chronic, relapsing disorder defined by compulsive drug seeking and use despite harmful consequences. It involves changes in brain circuits related to reward, stress, and self-control, which is why willpower alone is often not enough to overcome it.
- Dependence refers to a state of physical or psychological reliance on a substance. Physical dependence is marked by tolerance and withdrawal symptoms. You can be physically dependent without being addicted (e.g., a patient on long-term pain medication who experiences withdrawal if they stop, but who doesn't compulsively seek the drug).
- Overdose occurs when someone consumes a drug in quantities that exceed what the body can safely handle, potentially causing organ failure, respiratory arrest, or death.
- Rehabilitation involves structured treatment programs designed to help people overcome SUDs. These can include medical detox, behavioral therapy, support groups, and long-term aftercare planning.
- Harm reduction refers to practical strategies that aim to reduce the negative consequences of drug use without necessarily requiring abstinence. Examples include needle exchange programs (to prevent disease transmission), naloxone distribution (to reverse opioid overdoses), and supervised consumption sites.