caffeine coffee and nicotine cigarettes
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Substance abuse is an unfortunately common concern among people who have schizophrenia. As described in an April 2019 article in the journal Schizophrenia Research, 47% of people who receive treatment for schizophrenia have a substance use disorder. This is nearly three times higher than the rate of compulsive drug abuse among the general population.

The April 2019 article, which was authored by a team from Dartmouth University’s Geisel School of Medicine, reported the following estimated rates of substance use among people with schizophrenia:

  • Tobacco: 60%-90%
  • Alcohol: 21%-80%
  • Cocaine: 15%-50%
  • Cannabis: 17%-83%

The Dartmouth team also noted that elevated levels of co-occurring substance abuse and addiction are associated with increased levels of the following effects among people who have developed schizophrenia:

  • Worsening of clinical symptoms
  • Non-compliance with treatment
  • Substandard global functioning
  • Violent behaviors
  • Suicidal thoughts and actions
  • Elevated likelihood of relapse and re-hospitalization

It is no secret that addictions to alcohol and other dangerous substances can negatively impact a person’s life. Among people who have been diagnosed with schizophrenia, these types of substance abuse disorders can have the added effect of exacerbating their symptoms and complicating treatment.

But what about two other commonly used (and abused) substances? As indicated in the statistics from the Dartmouth study, as many as nine of every 10 people with schizophrenia may smoke cigarettes or use other tobacco products. Other studies have noted that people who have schizophrenia drink coffee at a significantly higher than average rate.

The prevalence of these habits has prompted several researchers to investigate how caffeine and nicotine may impact individuals who have schizophrenia.

Caffeine & Schizophrenia

According to an October 2020 study in the journal Clinical Schizophrenia & Related Psychoses, experts estimate that adults who have schizophrenia consume an average of 500 mg of caffeine every day. This is about three times higher than the typical daily caffeine intake among the general public.

The October 2020 study was conducted by a team from Halifax, Nova Scotia, Canada. The study was structured as follows:

  • It involved 27 subjects who were receiving outpatient treatment for either schizophrenia or schizoaffective disorder.
  • The subjects were between the ages of 18-55. All had been on a consistent medication regimen for at least four weeks. None had used illicit drugs for at least three months prior to the study.
  • The subjects were grouped according to caffeine use. Those who consumed 250 mg or less each day were in the moderate group, while those who used more than 250 mg per day were placed in the high group.
  • Subjects were assessed on a variety of issues related to cognitive functioning. This included working memory, visual learning and memory, sustained attention, processing speed, executive function, and verbal learning and memory.

The study’s findings included the following:

  • Subjects in the moderate caffeine group demonstrated a higher level of cognitive functioning.
  • Moderate caffeine users also performed better on a task that assessed executive functioning.
  • Individuals in the high caffeine group had fewer negative symptoms of schizophrenia and more positive symptoms than did the members of the moderate group.
  • Members of the high caffeine use group smoked more cigarettes and were more likely to be dependent on nicotine.
  • The use of sedating medications was not associated with higher levels of caffeine use.

Caffeine, Schizophrenia, & Gender

In December 2015, the journal Psychiatry Research published a study on the effects of caffeine on neurocognition among people with schizophrenia. This study found that caffeine may have a host of benefits for men who have schizophrenia. It also found one area of concern involving nicotine use among men who had been diagnosed with schizophrenia

The December 2015 study was conducted by a team from the University of Barcelona (Spain). It involved 113 subjects. 52 of the subjects had schizophrenia, while the other 62 – the control group – had not been diagnosed with any mental health disorders. The research team’s findings included the following:

  • Among the subjects who had schizophrenia, men typically consumed more caffeine than women did.
  • Test results indicated that caffeine helped men with schizophrenia perform better on “complex tasks requiring deeper cognitive processing.” The researchers clarified that this category included cognitive speed, working memory, visual memory, and semantic fluency.
  • Caffeine did not improve the performance of women with schizophrenia, nor did it lead to better results among either men or women in the control group.

Here are quick descriptions of the functions that the Spanish study assessed:

  • Cognitive speed involves how quickly a person can complete an assigned mental task. An assessment of cognitive speed tests a person’s ability to receive, interpret, and respond to information that is provided to them from an external source.
  • Working memory is an executive function that allows people to retain specific pieces of information for a short period of time so that they can use this information to perform a larger task or complete a complex project.
  • Visual memory is a perceptual capability that involves a person’s recall of images that had previously been presented to them.
  • Semantic fluency refers to a person’s ability to recall and use words from various categories. For example, during a semantic fluency test, a person may be given 60 seconds to say as many types of cars (or animals, or foods, or other objects from a specific category) as they can think of.

The Psychiatry Research study also found that nicotine use was associated with diminished semantic fluency among men who had schizophrenia. As with caffeine and cognitive processing, nicotine did not appear to affect semantic fluency among women with schizophrenia. Data on nicotine’s impact on semantic fluency among members of the control group proved to be inconclusive.

Nicotine & Schizophrenia

Nicotine’s effects on people with schizophrenia was a relatively small part of the Psychiatry Research study that we discussed in the previous section. Other researchers have taken a much more detailed look at this topic.

In June 2019, the journal BJPsych Advances published an examination of the association between tobacco (nicotine) and schizophrenia. This report, which was authored by two psychiatric experts from Sri Lanka, included the following findings:

  • The life expectancy of people with schizophrenia is 20 years shorter than among the general population. Cardiovascular disease, which is linked to smoking, is responsible for about two-thirds of all early deaths among people with schizophrenia.
  • Many professionals have theorized that people with schizophrenia smoke tobacco to counter the symptoms of the disorder and the effects of some medications. Research does not appear to support this theory. People who become dependent on nicotine typically experience an increase in positive symptoms, which leads to additional use of medication.
  • Nicotine use by people with schizophrenia has been linked to a greater intensity of negative symptoms, increased need for hospitalization, and “deterioration of thought disorder” over one to two years.
  • A study involving 61 people with treatment-resistant schizophrenia found that those who smoked tobacco scored lower on cognitive task assessments, had a larger number of negative symptoms, and were less successful at social adjustments than were subjects who avoided tobacco.
  • Four meta-analyses that involved more than 120 separate studies found that the risk of developing schizophrenia is significantly higher among smokers than among non-smokers.

To clarify that final point, the authors of the BJPsych Advances review noted that researchers found an elevated risk for schizophrenia among smokers, “even after adjusting for confounding factors such as comorbid cannabis use, socioeconomic status, and history of parental psychotic disorder and parental substance use disorder.”


Implications for Treatment

The studies cited in this article strongly suggest that quitting smoking and moderating caffeine use can yield significant benefits for people who have been diagnosed with schizophrenia. Though additional research is needed, it is difficult to argue with the findings that tobacco use and excessive caffeine consumption can undermine the quality of life of people who have schizophrenia. In the case of tobacco, the negative effects extend beyond diminished quality of life, as evidence has linked the use of this substance with an elevated risk of premature death.

Treatment approaches for schizophrenia that incorporate tobacco cessation assistance may benefit patients by easing the severity of negative symptoms and minimizing positive symptoms. If a person has already completed treatment for schizophrenia, but they continue to smoke, efforts by friends and family members to help them end this habit may also yield significant positive results in terms of both the quality and duration of their life.