Drug Dependence: Tolerance, Symptoms, Causes, Effects

Drug dependence is the physiological state in which repeated exposure has adapted the nervous system to a substance, so that the body needs the substance to run normally and produces withdrawal when the substance is reduced or removed. It is a body state rather than a behavior, and it develops without any intent on the part of the person it happens to.

Dependence has two observable markers, tolerance and withdrawal, and no third. Tolerance is the falling response to a fixed dose. Withdrawal is the set of signs and symptoms that appears as blood and tissue levels of the substance decline. The National Institute on Drug Abuse describes dependence as the result of physiological adaptations to chronic exposure to a drug, records tolerance as its companion, and states that dependence and addiction are not equivalent.

That last point is what this page turns on. The FDA records that physical dependence arises when benzodiazepines are taken steadily for several days to weeks, even as prescribed. A patient in that position has a body state to manage, not a diagnosis to answer for.

What Is Drug Dependence?

Drug dependence is a neuroadaptive state, defined by tolerance and by withdrawal on cessation, in which the nervous system has reset its own baseline around the continued presence of a substance. Removing the substance exposes that reset baseline, and the exposure of it is what withdrawal is.

Dependence is not measured by dose, by legality, or by how the substance was obtained. It is measured by what the body does when the substance stops arriving. Under DSM-5-TR, tolerance and withdrawal are criteria 10 and 11 of the 11 that define a substance use disorder, and both are excluded from the count when the medication is taken as prescribed. Dependence therefore sits inside the diagnostic system as evidence rather than as a verdict.

The mechanism behind that reset baseline is specific and measurable.

What Causes Drug Dependence?

Drug dependence is caused by repeated exposure driving counter-adaptation in the receptor systems the substance acts on, so that ordinary function now requires the substance to be present. Frequency and dose set the pace, and inherited variation sets how far and how fast an individual travels.

The National Institute on Drug Abuse describes the adaptation in the reward circuit directly: the brain of someone who misuses drugs adjusts by producing fewer neurotransmitters in that circuit, or by reducing the number of receptors that receive signals. The result is the effect known as tolerance, in which larger amounts are needed to produce the familiar effect. The same counter-adaptation that blunts the drug's effect is what leaves the system unopposed once the drug is withdrawn.

The 4 contributors below each carry a named federal source.

• Repeated pharmacological exposure drives the receptor and neurotransmitter changes NIDA describes, which produce tolerance first and withdrawal on cessation second.
• Frequency and duration of use set the timeline. NIDA records that short-term medical use of opioid pain relievers lasting days rarely leads to an opioid use disorder, while regular use across weeks or longer leads to dependence and tolerance.
• Inherited variation shapes individual risk. NIDA estimates that genes, including the effects environmental factors have on gene expression, account for between 40 and 60 percent of a person's risk of addiction. That estimate is published for addiction rather than for physical dependence.
• Long-term therapeutic use produces the same adaptation as any other exposure. NIDA lists tolerance, hyperalgesia and addiction among the risks of long-term opioid treatment, and the FDA places benzodiazepine physical dependence at several days to weeks of steady use, even as prescribed.

Tolerance appears first in that sequence, and it is routinely mistaken for dependence itself.

What Is The Difference Between Drug Tolerance And Drug Dependence?

Tolerance is a reduced response to a fixed dose, and dependence is the withdrawal state that appears once the substance is removed. Tolerance is measured while the substance is present. Dependence is measured by what happens when it is not.

The two travel together without being the same thing. The National Institute on Drug Abuse records tolerance, the need to take higher doses of a medication to get the same effect, as a companion of dependence rather than a synonym for it, and names the clinical problem this creates: once tolerance appears, a physician has to separate a developing drug problem from a genuine medical need for a higher dose. The gradations, mechanisms and clinical management of tolerance itself are set out in the guide to drug tolerance and its causes.

How Quickly Does Physical Dependence Develop?

Physical dependence develops over days to weeks for benzodiazepines and over weeks or longer of regular use for opioids, on the timelines the FDA and the National Institute on Drug Abuse publish. No single figure covers every substance, because each authority states an interval only for the class it governs.

The 5 substance classes below each carry a statement from a named regulator or institute about how dependence develops in that class and about what withdrawal from it involves.

Substance class	What the named authority states about onset	What the same authority states about withdrawal
Benzodiazepines	FDA, 2020 Boxed Warning update: physical dependence arises when benzodiazepines are taken steadily for several days to weeks, even as prescribed	FDA: stopping abruptly or reducing the dosage too quickly can result in withdrawal reactions, including seizures, which can be life-threatening
Opioids	NIDA: short-term medical use lasting days rarely leads to an opioid use disorder, while regular use across weeks or longer leads to dependence and tolerance	NIDA: restlessness, muscle and bone pain, insomnia, diarrhea, vomiting, cold flashes with goose bumps, and involuntary leg movements
Alcohol	NIAAA publishes no onset interval. It records withdrawal as occurring when someone who has been drinking heavily for a prolonged period suddenly stops	NIAAA: a potentially life-threatening process, accounting for approximately 260,000 emergency department visits and 850 deaths in the United States each year
Barbiturates	NIDA: continued use of CNS depressants, the class that includes barbiturates, leads to dependence and to withdrawal when use is abruptly reduced or stopped	NIDA: withdrawal from prolonged barbiturate use carries life-threatening complications
Nicotine	DiFranza and colleagues, 2007: of 217 adolescents who inhaled from a cigarette, 127 lost autonomy over their tobacco use, a measure of diminished control rather than of physical dependence, 10 percent of them within 2 days of first inhaling and 25 percent within 30 days	DiFranza and colleagues: withdrawal symptoms and failed cessation attempts can precede daily smoking

Those intervals describe when dependence arrives. What it looks like once present is a separate list.

What Are The Symptoms Of Drug Dependence?

The symptoms of drug dependence are a rising dose requirement, a falling drug effect, and a withdrawal syndrome that appears as the substance clears. The behavioral items that surround those three on a published symptom list belong to the diagnostic criteria for a substance use disorder instead.

The 3 core symptoms below are the ones a clinician records as evidence of physical dependence.

1. Increased dose requirement, in which the amount that produced an effect no longer produces it and the dose climbs to compensate.
2. Diminished effect at the previous dose, which is the same adaptation observed from the other direction.
3. Withdrawal on reduction or cessation, with a symptom set specific to the substance class, running from restlessness and muscle pain for opioids through to seizures for benzodiazepines and alcohol.

The full symptom picture during cessation, across every class and timeline, is set out in the guide to drug withdrawal symptoms and treatment.

What Happens When A Dependent Person Stops Taking The Drug?

Withdrawal begins as blood and tissue levels fall, and for alcohol, benzodiazepines and barbiturates it carries a risk of seizures and death. Cessation from those three classes is a medical event rather than a decision a person acts on alone.

Call 911 immediately for a seizure, a collapse, a loss of consciousness or a confused and agitated state during withdrawal from any substance. Call Poison Help at 1-800-222-1222 for any ingestion or overdose. Never stop a prescribed opioid, benzodiazepine or barbiturate without a taper schedule from the prescriber, and never restart at the old dose after a break in use.

The scale of the alcohol case is documented. The National Institute on Alcohol Abuse and Alcoholism describes alcohol withdrawal as a potentially life-threatening process that occurs when someone who has been drinking heavily for a prolonged period suddenly stops, and its Core Resource on Alcohol puts the annual United States burden at approximately 260,000 emergency department visits and 850 deaths. For benzodiazepines, the FDA Drug Safety Communication of 23 September 2020 states that stopping abruptly or reducing the dosage too quickly can result in withdrawal reactions, including seizures, which can be life-threatening.

What Are The Effects Of Long-Term Drug Dependence?

Long-term dependence raises the dose a person needs, converts stopping into a supervised medical procedure, and opens a lethal window after any period of abstinence. All three follow from the same adaptation, and the third one kills people who believe they are past the danger.

The 3 effects below follow from the physiology rather than from the behavior around it.

• Escalating exposure. Tolerance raises the dose needed for a given effect, and a higher dose raises exposure to every other toxic property the substance carries.
• Constrained cessation. Withdrawal makes unsupervised stopping unsafe for alcohol, benzodiazepines and barbiturates, so the exit from dependence runs through a prescriber rather than around one.
• Lost tolerance after a break. The National Institute on Drug Abuse states the danger directly: a person who uses as much of the drug as they did before quitting can easily overdose, because the body is no longer adapted to the previous level of exposure. Call 911 and Poison Help at 1-800-222-1222 for any suspected overdose.

None of those three establishes that a disorder is present, which is the distinction the next section holds.

Is Drug Dependence The Same As Addiction?

No. Dependence is a physiological adaptation, and addiction is a disorder scored against 11 diagnostic criteria of which tolerance and withdrawal are only two. A person tapering off a correctly prescribed opioid is dependent while meeting no criteria at all.

DSM-5-TR settles the question in a footnote to its own criteria: tolerance and withdrawal in the context of appropriate medical treatment, meaning pain medication used as prescribed, do not count toward a substance use disorder. The full criteria set, the severity bands, the history of the two words and the question of which term applies to a given person are set out in the comparison of the key clinical differences between drug abuse and drug dependence. The behavior pattern on the other side of that comparison is covered in the guide to drug abuse symptoms and causes.

How Is Drug Dependence Treated?

Physical dependence is treated by a prescriber-directed taper, with the reduction schedule set by the substance, the dose and the duration of use. Where a substance use disorder is present alongside the dependence, the taper is one component of a treatment plan rather than the whole of it.

Three things separate a taper from a decision to stop. The schedule is written in advance rather than improvised during withdrawal. The setting is matched to the seizure risk of the substance class, which is why alcohol, benzodiazepine and barbiturate cessation is medically supervised. And the plan accounts for what follows the taper, because lost tolerance makes a return to the previous dose dangerous. Where a criteria count establishes a substance use disorder as well, the assessment that sets the matching level of care is described in the guide to the levels of care in addiction treatment.

What Are The Most Common Questions About Drug Dependence?

The 6 questions below cover prescribed medication, reversibility, the shortest onset interval, whether dependence is permanent, psychological dependence, and quitting without help.

Can A Person Be Dependent On A Medication A Doctor Prescribed?

Yes. The FDA states that physical dependence arises when benzodiazepines are taken steadily for several days to weeks, even as prescribed. DSM-5-TR does not count tolerance or withdrawal as diagnostic criteria in that situation.

Does Drug Dependence Reverse?

Yes. Physical dependence resolves once the substance is withdrawn on a prescriber-directed schedule. NIDA records that withdrawal symptoms range from mild to severe depending on the drug, and that slowly tapering the dosage can usually manage or avoid them.

Which Drugs Produce Dependence Over The Shortest Interval?

The FDA places benzodiazepine physical dependence at several days to weeks of steady use, even as prescribed. That is the shortest interval any authority cited on this page states for a prescribed class.

Is Dependence Permanent?

No. Physical dependence resolves after a completed taper. Tolerance falls with it, and that fall is what makes a return to a previous dose dangerous rather than harmless.

What Is Psychological Dependence?

Psychological dependence is the craving and loss of control that sits in the behavioral criteria rather than in the pharmacologic pair. Both forms sit inside one diagnosis under DSM-5-TR.

Is It Safe To Quit Without Medical Help?

Not for alcohol, benzodiazepines or barbiturates. Withdrawal from those three classes carries a documented risk of seizures and death. Contact a prescriber before any reduction, and call 911 for a seizure.