To what extent is control over when a substance is used relevant to addiction?

Question

For example, let's say someone uses X amount of heroin a week, and no more than Y a day. If somehow their arm is connected to a device that randomly (unpredictably, but within their "waking leisure hours") administers heroin at no more than Y a day and X per week, would users feel as addicted or dependent on the substance? Or would the loss of control, not even necessarily being able to look forward to using the substance every day or at a certain time or after certain events or feelings, make it not nearly as satisfying or addictive?

Answer 1

This is a tough question to answer definitively. I won't address heroin specifically but rather drugs of abuse more generally since a lot of the addictive patterns are the same and heroin is less often studied in the lab.

I am not aware of studies that specifically use the protocol you are describing in human subjects; although you might be able to make some inference based on drug seeking behavior after hospital administration of opiates, for example.

However, in animal studies, drug sensitization protocols have been used where animals are given injections of some drug, and later are allowed to self-administer the drug. Typically, animals who were previously given injections of the drug are quick to develop self-administration habits compared to unexposed animals. It's hard to ask an animal what they "feel" and this may not be the same as "feeling addicted/dependent" but at least when they have an opportunity to self-administer they are more prone to take the opportunity.

This effect is sensitive to the particulars of the experiment, though: Higher self-administration doses don't show the effect (because undosed animals also quickly develop a habit). Limited exposure tends to create less or absent sensitization. Sensitization effects tend to be easier to detect when animals have to work harder for subsequent doses in a progressive ratio paradigm; on a fixed ratio paradigm the differences are minor or non-existent.

A great experiment to most directly address your question would be to dose one animal according to the self-administration patterns of another and compare them on addictive behaviors; however, one difficulty in such a comparison is that the animals that haven't been dosing themselves still need to learn how to dose themselves. I am not aware of a study that has done this but I hope if it has been done someone else can point it out!

---

Ferrario, C. R., Gorny, G., Crombag, H. S., Li, Y., Kolb, B., & Robinson, T. E. (2005). Neural and behavioral plasticity associated with the transition from controlled to escalated cocaine use. Biological psychiatry, 58(9), 751-759.

Lett, B. T. (1989). Repeated exposures intensify rather than diminish the rewarding effects of amphetamine, morphine, and cocaine. Psychopharmacology, 98(3), 357-362.

Lorrain, D. S., Arnold, G. M., & Vezina, P. (2000). Previous exposure to amphetamine increases incentive to obtain the drug: long-lasting effects revealed by the progressive ratio schedule. Behavioural brain research, 107(1-2), 9-19.

Mendrek, A., Blaha, C. D., & Phillips, A. G. (1998). Pre-exposure of rats to amphetamine sensitizes self-administration of this drug under a progressive ratio schedule. Psychopharmacology, 135(4), 416-422.