People who become addicted to a particular drug (e.g., heroin) are more likely to develop dependence to other drugs within the same drug class (e.g., prescription painkillers) — a problem known as cross-addiction. Cross-addiction is common in today’s world of addiction — heroin addicts are becoming addicted to prescription opioids (e.g., oxycodone, hydrocodone), and cocaine addicts are starting to abuse prescription stimulant medications (e.g., Adderall, methylphenidate).
Why does tolerance matter?
Tolerance develops when a person uses alcohol or drugs repeatedly or over a long period of time and no longer responds to a drug in the same way they initially responded, which can rapidly develop for a patient taking opioid analgesics (i.e., prescription pain medications). A person who develops tolerance becomes physically dependent on the substance and requires more of the drug to achieve the desired effect.
In the case of opioid pain medications, tolerance to the substance develops as the pain receptors, or the sites where the drugs bind to produce analgesic effects (i.e., pain relief), become less responsive and sensitive to the drug. As tolerance develops, patients may begin ingesting higher and more dangerous doses of a substance to achieve the same level of initial response.
These individuals are more likely to develop cross-addiction, which occurs when a person develops tolerance (i.e., physical dependence) on one substance, making them more likely to develop an addiction to another drug in the same drug class. The tendency for an illicit drug user to seek out similar drugs occurs because the drugs have similar, if not identical, mechanisms of action and affect similar areas of the brain.
The problem of opioid tolerance and addiction
People with illicit drug abuse or dependence may take similar-acting drugs for many different reasons — prescription painkillers are more available, cheaper or easily accessible than heroin. Sometimes, heroin users will take prescription opioid medications to relieve the withdrawal effects that occur when trying to reduce or stop taking an illicit drug. As heroin and opioids are both in the same drug class, opioid prescription medications can prevent some of the negative withdrawal symptoms from occurring when a person stops taking heroin.
On the other hand, people who also take prescription pain medications for non-medical reasons are also more likely to try heroin within the next 10 years. As tolerance develops for drugs in the same drug class, they can essentially switch back and forth between drugs, developing even a higher tolerance for opioids as they take more and more of the substance to achieve the desired effect. Unfortunately, heroin is a much more addictive drug, as heroin users are three times as likely to develop opioid dependence, and 54 percent of heroin users develop dependence, while only 14 percent of people using opioid prescriptions non-medically will develop dependence.
During pain medication management, people can develop tolerance to their prescribed dose, even when taking their medications as prescribed. Due to lower perceptions of harm associated with doctor-prescribed pain medications compared to heroin and other illicit drugs, patients who develop tolerance may begin taking higher doses than prescribed. In 2010, 1 in 20 people used prescription pain medications when it was not prescribed for them or took larger doses than prescribed.
Recent research highlights the concerns of legitimate medicinal use of prescribed opioid pain medications during adolescence and young adulthood as a pathway to later misuse opioids and develop opioid use disorders in adulthood. This new study used data from the National Institute for Drug Abuse (NIDA)-funded Monitoring the Future survey of adolescent drug use, and attitudes showed that teens who received a prescription for opioid pain medication by Grade 12 were at 33 percent increased risk of misusing an opioid between ages 19 and 25.
Benefits of opioid cross-tolerance
Despite being a major contributor to the cross-over of addiction from illicit drug use to prescription drugs, the concept of cross-addiction has, on the other hand, been beneficial to the development of pharmacological treatments, including medication-assisted treatment and opioid maintenance therapies, for detoxification (i.e., reducing symptoms of withdrawal) and treatment purposes of opioid-related disorders (i.e., intoxication, overdose and withdrawal).
Scientists have developed prescription drugs that act in the same manner as certain addictive opioid drugs to reduce withdrawal effects of persons in treatment for addiction to opioids. While methadone maintenance therapy (MMT) has been the standard of care for more than 30 years, the recent use of buprenorphine maintenance therapy (BMT) for treating opioid dependence has revolutionized the treatment of opioid dependence for patients across the country. Buprenorphine not only suppresses withdrawal and cravings, but it also causes no additional effects at higher doses and is considered to be safer than methadone, which can lead to fatal consequences during an overdose.
Furthermore, an intranasal and injection form of opioid antagonist, naloxone, was recently approved by the Federal Drug Administration (FDA) to block or reverse the life-threatening respiratory and sedative effects of opioid overdose.
The tendency for illicit drug users to seek out prescription drugs in the same category as their illegal drug of choice can lead to problems like cross-addiction when a person addicted to heroin seeks out opioid prescription painkillers such as OxyContin due to the similar analgesic effects produced by both drugs.