Tolerance, Dependence, and Addiction
The Body Can Adapt to Substances
Tolerance, dependence, and addiction are related processes that are often confused for one another, however, each is distinct in very important ways. While all occur from repeated use of a substance, the response in the body is different.
Tolerance is very common with long-term opioid use, and decreases its therapeutic effects over time, posing heightened risks of misuse, dependence and addiction.
Tolerance
Tolerance is the process of the body adapting to a substance over time. When opioids are used on a regular basis, the nervous system reduces its responsiveness to receptor activation, and the same dosage of the drug will produce less of an effect. A person developing tolerance to opioids experiences reduced effects when taking a stable dose, and may increase their intake to replicate earlier effects. This can escalate use, and presents additional risk for dependence and addiction.
Tolerance to an opioid will decrease if the drug is not taken for a significant period of time. Because of this decreased tolerance, individuals who have discontinued use are more vulnerable to opioid overdose and death if they resume use at high dosages.
Dependence
With repeated use, the nervous system adapts to function normally under the effects of the substance. The absence of the substance causes physiological reactions, such as sweating, constipation, confusion, and nausea. This functional reliance on substances is known as dependence, and the symptoms experienced in a drug’s absence are known as withdrawal. Symptoms of withdrawal are both physical and mental, and can range from mild to life-threatening.
Dependence is an outcome of increased tolerance, and can occur with either medical or recreational use of a substance. An individual who has developed dependence will likely need to reduce medications gradually to avoid withdrawal symptoms; this process of slowly decreasing a dosage is called tapering. A person can develop tolerance or dependence on a drug without developing an addiction, but these stages present elevated risk of an eventual use disorder.
Addiction
Addiction, or substance use disorder, is when a person continues using drugs or alcohol despite the impact on other areas of their life at work, at school, or at home. Compulsive use, despite negative consequences, is a key indicator of addiction. Unlike tolerance and dependence, addiction is a disease with physical, mental and behavioral aspects. Behaviors that indicate an addiction include:
- Not adhering to the prescribed schedule for the drug
- Taking more than one dose at a time
- Repeated reports of stolen or lost drugs
- Doctor shopping (getting the drug from more than one doctor)
- Isolation
- Additionally using non-prescribed psychoactive drugs
- Using pain medications for sedation, intoxication, to boost energy, or to lower anxiety levels
- Requesting certain formulations or routes of administration of the drug
- Avoidance of or disinterest in non-opioid treatment options