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Cannabis May Increase the Likelihood of Amotivational Syndrome

Understanding how cannabis can blunt the reward system.

Key points

  • Motivation is a subjective experience and therefore extremely difficult to measure objectively.
  • Motivational syndrome has long been seen as a sign of cannabis addiction, but has only recently been measured.
  • Liking and wanting are two different forces. Drug use changes the brain in ways that stimulate wanting the drug.

Until recently, I ignored the idea of a cannabis-induced amotivational syndrome. Of course, I was familiar with the stereotypical view of potheads couch-locked into immobility, but this could have a variety of causes other than amotivational syndrome. Besides, I could not imagine how motivation could be measured objectively.

A legendary exercise demonstrating the difficulty of measuring motivation was often used by the gestalt therapist Fritz Perls. He handed a pillow to people and asked them to pantomime trying to drop it. Despite whatever contortions people went through, they continued to hold the pillow. There was no convincing way they could objectively portray their intention to drop the pillow. Motivation is an internal, largely subjective experience.

Then Meghan Martz[1], at the University of Michigan, published research that changed my mind. Martz used a delayed monetary reward protocol, which means people were given a simple computer task that promised cash rewards at the end of the test—a low monetary reward for poor performance and a higher reward for better performance. While watching the computer screen and pressing a button whenever a stimulus appeared, and before any money was received, Martz used functional magnetic imaging (fMRI) to measure activity in a small part of the brain called the nucleus accumbens, the reward center. She tested individuals three times, at ages 20, 22, and 24. She also recorded their report of marijuana use at each age.

Her data showed that, while everyone at age 20 had the same level of reward center activation in anticipation of the cash reward, those who most increased their cannabis use over the next four years showed progressively less activation at ages 22 and 24. Cannabis users no longer viewed cash with as much anticipation of the reward. Martz concluded that the effects of long-term cannabis use results in a general blunting of reward response. While it could be argued cannabis produces enlightenment and freedom from materialistic desires, a deeper look at nucleus accumbens functioning points in other directions.

First, the word “reward” should not be interpreted as pleasure. Evolution gave rise to the nucleus accumbens in order to increase the likelihood of survival. Behaviors such as exercise, eating, and sexual activity pump dopamine into the nucleus accumbens. Increased dopamine means the behavior producing it is more likely to be repeated. Unfortunately, every addictive drug—from caffeine to alcohol, opiates, stimulants, Xanax, and cannabis—pumps up to 10 times as much dopamine into the nucleus accumbens than mere behaviors do. More dopamine in the nucleus accumbens means more repetition of the drug. This is the basic physical mechanism of addiction.

Second, drug-induced, higher-than-normal levels of dopamine change the cellular architecture of the nucleus accumbens. This changed structure changes what is rewarded, and therefore what is important enough to be valued and sought. We call this “salience.”

Third, the salience of any stimulus determines its quality of being particularly noticeable, important, and desirable. When we are hungry, the salience of smells wafting out of a bakery is far greater than when we are hurrying to get to an appointment. Martz demonstrated that the salience conferred by the nucleus accumbens onto a delayed cash reward had diminished over time for regular cannabis users. This would have an obvious impact on motivation, ergo an amotivational syndrome based on reward deficit. Blunted anticipation of reward would certainly unmotivate most of us.

Research has elucidated a difference between what can be called “liking” and what can be called “wanting”, which are related respectively to pleasure and repeating.[1] A simple experiment makes the distinction. If a rat is given a choice between sugar water or water laced with cocaine, it will usually choose the sugar water. It prefers, or “likes” the sugar more. However, if rats are only given either sugar water or cocaine water and then each is removed, they will continue pressing the cocaine lever far more often than they will the sugar lever. They “want” cocaine more than sugar. Rats may prefer (i.e., like) sugar water more, but they will work harder (i.e., want) the cocaine water more. This distinction is relevant to what is meant by both motivation and addiction.

Are we to conclude that the mind is a prisoner to the brain? To some degree, yes. The mind is essentially the result of brain function. However, although we cannot stop the brain’s wanting, our mind can use understanding and acceptance to recognize that our brain is out of control, and the grit that comes from preferring (i.e., liking) inclusion in a supportive community to bend behavior toward abstaining from drugs that induce repetitive wanting.

Recovery is a decision by our mind and spirit that also requires changes in behavior. Without changing behavior, the brain’s craving will defeat the mere desire to experience the freedom of recovery. Motivation to recover demonstrates the complexity of its provenance. Without the desire for a healthy recovery, and the hard work to achieve it, the blunting of reward and resultant amotivational syndrome induced by cannabis can impact the trajectory of a person’s life.


1. M. E. Martz, et al. Association of Marijuana Use With Blunted Nucleus Accumbens Response to Reward Anticipation. JAMA Psychiatry,2016; 73(8): 838–44.

2. K. C. Berridge. Food Reward: Brain Substrates of Wanting and Liking. Neurosci Biobehav Rev, 1996;(1): 1–25.21!