“On the effects of coffee”,Hahnemann’s comment versus Modern scientific studies on Coffee- A Review Article

Dr Meenu Priya A

Objectives: To describe the various modern scientific studies on coffee in comparison with Hahnemann’s understanding on the effects of coffee. Methodology: Various observational and interventional studies reported on coffee consumptions and its health outcome were studied for the co-relation with Hahnemann’s article “On the effects of Coffee” Results: A total of 13 articles were reviewed along with Hahnemann’s writing which showed 7 modern study findings were in positive association with Hahnemann’s writing, 3 with negative association and 3 with no association. Conclusion: The review concludes that there are both positive and negative association and of which the maximum is positive association of Hahnemann’s writing with the findings of Modern scientific studies which shows the relevance of Hahnemann’s writing in today’s scientific world. There is need for more interventional studies to validate the findings of this review article.

One of the most common beverages that is consumed worldwide is coffee. Epidemiological studies and Experimental research have suggested that coffee consumption is associated with reduced risk of several chronic and degenerative diseases1 which is in much contrary with the writing of Hahnemann’s “On the Effects of Coffee, from original observations” which was published in 1803 in Leipzig. 2 This review article aims to find an association between the findings of modern scientific studies on coffee and Hahnemann’s writing on coffee.

Various articles are reviewed to understand the findings with respect to effect of coffee on a certain category such as respiratory system, sleep, memory etc., and is compared with the writing of Hahnemann to know if there is any positive or negative association with the study findings.

The categories and reviewed articles are as follows:

Mind and Memory:2,3,4

According to Hahnemann, the symptoms coming up immediately after consumption of coffee in the faculty of mind and memory are as follows,

  • Spring of memory immediately after taking coffee
  • Loquacity
  • Hurried chattering
  • Letting things escape from our lips that we ought not to have spoken about
  • Over-hasty disclosures
  • Hurried resolves
  • Immature judgements
  • Frivolity
  • Changeableness
  • Irresolution
  • Flighty mobility of the muscles, without the production of any durable impression
  • Theatrical behaviour2

A randomised, placebo-controlled, double-blind, counterbalanced-crossover study was conducted to compare the effects of regular coffee, decaffeinated coffee and placebo on measures of cognition and mood. 72 participants were included in the study of which 59 were considered for analysis The parameters of mood cognition included for analysis were, Digit vigilance accuracy and reaction time, Rapid visual information processing, Computerised location learning delayed trial, Alertness, Tiredness, Headache, overall mood, Mental fatigue, Jittery. The results of the study showed that the regular coffee produced the expected effects of decreased reaction time and increased alertness when compared to placebo. Increased digit vigilance accuracy, decreased tiredness and headache ratings were observed when compared to decaffeinated coffee. Higher jittery ratings were seen in younger females and older males who were on regular coffee. The study concluded that the behavioural activity of coffee is beyond its caffeine content, and raising issues with the use of decaffeinated coffee.3

A prospective, interventional, comparative study was conducted on 70 healthy individuals to explore and compare the acute effects of decaffeinated and caffeinated coffee on reaction time, mood and skeletal muscle strength in healthy volunteers. The parameters assessed were reaction time by digital display multiple-choice apparatus, mood by Visual Analogue Scale (VAS) and Profile of Mood states revised version (POMS) and skeletal muscle strength by hand dynamometer. The results of the study showed that there was statistically significant change (p<0.005) in reaction time and mood (VAS, POMS) from the baseline in both the groups. Both the groups did not show any significant effects on skeletal muscle strength. Caffeinated coffee group showed higher and significant improvement of mood when compared to decaffeinated coffee.4

Gastro-intestinal symptoms2,5,6
According to Hahnemann, the gastro-intestinal symptoms excited by coffee are, “More rapid peristaltic movements, force their contents but half-digested more quickly towards the anus, and the gourmand imagines he has discovered a splendid digestive agent. But the liquid chyme which serves to nourish the body, can in this short time neither be properly altered (digested) in the stomach, nor sufficiently taken up by the absorbents in the intestinal canal; hence the mass passes through the unnaturally active bowels, without parting with more than the half of its nutritious particles for the supply if the body, and arrives at the excretory orifice still in a half-liquid state. Of a truth, a most excellent digestive agent, far surpassing nature! Moreover, during the evacuation itself the anus is excited by the primary action of the coffee to more rapid dilatation and contraction, and the faeces pass out soft, almost without effort, and more frequently than in the case of healthy individuals who do not partake of coffee”.2

A Systematic Review and Meta-Analysis of Prospective Study was conducted to provide an updated synthesis of the relationship between coffee consumption and the risk of colorectal cancer. 26 prospective studies were included for the review. Regarding colorectal cancer, no significant relationship was detected. Stratifying for ethnicity, a protective effect emerged in US subjects. Concerning colon cancer, coffee proved to exert a protective effect in men and women combined and in men alone. Stratifying for ethnicity, a significant protective effect was noted in European men only and in Asian women only. Concerning rectal cancer, no association was found. Decaffeinated coffee exhibited a protective effect against colorectal cancer in men and women combined. However, little is known about the relationship between the genetic make-up and the risk of colorectal cancer associated with coffee.5

 A systematic review with meta-analysis of six randomized controlled trials to investigate the efficacy of providing coffee to elective abdominal surgery patients, immediately postoperatively, to lessen postoperative ileus. The result of the study showed that coffee was statistically significant in shortening the time between surgery and the first passage of stool (mean difference, 9.38; 95% confidence interval, 17.60 to 1.16; P ¼ .03). Although not statistically significant (P ¼ .20), the overall effect favoured shorter hospital stays for those patients’ receiving coffee. The study concluded that coffee given as early as 2 hours postoperatively decreases time to first bowel movement and also tolerated solid food faster and were discharged sooner.6

Respiratory Symptoms2,7,8
According to Hahnemann, the respiratory symptoms that come after chronic consumption of coffee are, “Viscid mucus rattles in their chest as they breathe, especially when they are asleep, which no amount of coughing can remove: they have always got a wheezing at the chest”2

A hospital based large prospective cohort study was conducted to investigate the association of coffee and green tea intake and pneumonia among the Japanese elderly of over 65years old, newly diagnosed as Pneumonia. The study included 199 cases and 374 controls. The results of the study showed that the Odds Ratio (OR) of those who do not drink coffee with those who drink less than one cup of coffee per day was 0.69 (95% CI 0.39-1.21), with those who drink one cup per day was 0.67(0.38-1.18) and those who drink two or more cups was 0.50 (0.28-0.88) (p=0.024). The study suggested that there is a preventive association between coffee intake over 2 cups per day and pneumonia in the elderly.7

 A Systematic review was conducted to know the effects of coffee consumption on a wide range of non-malignant respiratory outcomes such as incidence, prevalence, evolution or severity of respiratory disease. 15 studies were included for the review of which seven were cohort, six were cross-sectional, one was case-control and one was randomized control trial. The results were the following, the reduction in prevalence of Asthma was associated with coffee consumption. The case- control study showed that there was higher risk of COPD with Coffee consumption. One study showed that Coffee with natural honey was an effective treatment for persistent post-infectious cough. One study found that coffee was associated with reduction in respiratory mortality and one study found improved lung function in coffee consumers. In most of the studies, smoking was a significant confounder. The study concluded that there were some positive effects on the respiratory system through coffee consumption and may be a part of a healthy lifestyle in turn reducing the respiratory morbidity.8

 Sexual sphere2,9,10

According to Hahnemann, the sexual symptoms are excited by primary action of coffee more than by any other artificial means. They are,

  • Arising of voluptuous images in mind
  • Excitation of genitals to complete ecstasy
  • Unrestrainable ejaculation of semen
  • Sexual desire excited too soon in the tenderest, immature age in both sexes
  • Has the most perceptible influence on morality
  • Early impotence as a natural consequence

A prospective cohort study was done to investigate the association of coffee intake with incidence of Erectile Dysfunction (ED). An analysis of 21,403 men aged 40-75 years was conducted using the Health Professionals Follow-up Study. Total coffee, regular and decaffeinated coffee intakes were self-reported on food-frequency questionnaires. The results of the study showed that  there is no significant differences for incident ED after comparing highest (≥ 4 cups/day) with lowest category (0 cups/day) of total- (HR = 1.00; 95% CI: 0.90 – 1.11) and regular- coffee intakes (HR = 1.00; 95% CI: 0.89 – 1.13) and for decaffeinated coffee intake, after comparing the highest category with lowest category, 37% increased risk of ED (HR = 1.37; 95% CI = 1.08-1.73) was found with a significant trend (Ptrend = 0.02) and hence the long-term coffee intake was not associated with the risk of ED.9

An interventional mating trial was conducted on Male Queensland Fruit Fly (Q-Fly) to demonstrate potential of pre-release caffeine supplements as a novel means to accelerate sexual maturation in Male Q-fly.  The results of the study showed that analytical caffeine was very effective at accelerating sexual maturation, while no positive effects of caffeine-containing instant coffee or guarana supplements were detected. In parallel, development of testes and ejaculatory apodemes was accelerated in males provided analytical caffeine but not instant coffee or guarana. High doses of guarana and instant coffee reduced longevity while even the highest doses of analytical caffeine did not affect longevity. The study concluded that Pre-release caffeine supplements promote sexual maturation in Q-flies.10

According to Hahnemann, the skin symptoms that come up who consumes an immoderate amount of coffee are as follows,

  • Circumscribed redness of cheeks
  • Warmth and moistness of forehead and palms
  • Feels warmer, agreeably, yet uneasily warm than before
  • Warmth never comes to the length of heat. No one ever becomes burning hot.2

A randomized, double-blind, placebo-controlled crossover study was conducted to investigate if intake of caffeine containing coffee changes blood flow and microvascular reactivity in the skin. Acute changes in cutaneous vascular conductance (CVC) in the forearm and the tip of the finger, the microvascular response to transdermal iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) and post-occlusive reactive hyperaemia (PORH) in the skin, after intake of caffeinated or decaffeinated coffee was measured. The results of the study showed that there was significantly stronger Vasodilatation during iontophoresis of ACh after intake of caffeinated coffee compared to after intake of decaffeinated coffee (1.26 ± 0.20 PU/mmHg vs 1.13 ± 0.38 PU/mmHg). CVC before and after PORH were not affected by caffeinated and decaffeinated coffee. After intake of caffeinated coffee, a more pronounced decrease in CVC in the fingertip was observed compared to after intake of decaffeinated coffee (-1.36 PU/mmHg vs. -0.52 PU/mmHg, P = 0.002). the study concluded that Caffeine acutely improves endothelium-dependent microvascular responses in the forearm skin, while endothelium-independent responses to PORH and SNP iontophoresis are not affected. Blood flow in the fingertip decreases 11

Bone Mineral Density2,12
According to Hahnemann, “an inordinate indulgence in coffee has for its secondary effect excites a great tendency to caries of bones”

A cohort study was done to identify coffee-associated metabolites and evaluate their association with Bone mineral Density (BMD). Two independent cohorts totalling 564 healthy community-dwelling adults from the Hong Kong Osteoporosis study who visited in 2001-10 (N=329) and 2015-16 (N=235) were included. Analyses of association was done by Multivariable linear regression and robust regression. 12 serum metabolites were positively correlated with coffee consumption after Bonferroni correction for multiple testing (p<4.87 x 10-5). Habitual coffee intake was positively and significantly associated with BMD at the lumbar spine and femoral neck. The study concluded that 12 metabolites were significantly associated with coffee intake and could be potential biomarkers of coffee consumption and affects bone health.12

According to Hahnemann, the changes in sleep after consumption of coffee is explained in this way such as,

“After completing our day’s labour, we must, in the course of nature, become lazy; a disagreeable feeling of weight and weariness in our bodily and mental powers make us ill-humoured and cross, and compels us to give ourselves up to the requisite rest and sleep.

 This crossness and laziness, this disagreeable weariness of mind and body on the approach of natural sleep, rapidly disappears on taking this medicinal beverage, and a dispersion of sleepiness, a factitious liveliness, a wakefulness in defiance of nature occurs”2

A randomized, counterbalanced trial was conducted in sixty-nine participants to examine the effects of coffee on vigilance, comparing individuals based on recent sleep quality. The study included consumption of 237 ml of water or coffee (100mg caffeine), followed by a continuous performance test assessing vigilance at 30, 90 and 120min. The results of the study showed that coffee increased commission errors and only partially reduced omission errors in individuals reporting poor sleep quality. The use of coffee to combat poor sleep may therefore be detrimental in situations requiring inhibitory control.13

An integrative literature review was conducted to examine the evidence of relationship between caffeine consumption and subsequent quality and quantity of night time rest and to examine evidence of whether performance deficits caused by sleep deprivation linked to caffeine can be reversed by caffeine consumption during the subsequent daytime period and to examine the net caffeine effect on daytime functioning. The review concluded that there is a range of positive impacts of caffeine consumption on both physical and cognitive functioning. Animal and well-controlled human studies tend to confirm a “net benefit” for caffeine use and has applied advantages as a “performance enhancer”14

On Discontinuing the use of Coffee2,15

Hahnemann’s suggestion and advice as to ways of how to discontinue the use of coffee are as follows

  • Convince patient of the urgent and indispensable necessity of discontinuing the use of coffee
  • If the physician has achieved this objective of convincing the patient, the further advice can be given
  • The quantity of coffee taken be reduced by a cup every three or four days
  • Allow the last breakfast cup to be continued for a week longer
  • After which, allowed to be left at once or it may be continued on every alternate day for another week, according to circumstances
  • If the person/ patient is reliable, the object can be achieved in about 4 weeks
  • But if the person is faint-hearted and indecisive, allow a cup of tea for a week for every cup of coffee that we take away
  • Gradually reduce tea intake and substitute it with warm milk for breakfast
  • Along with the breaking off the habit, body should be refreshed and strengthened by daily walks in open air
  • Indulge in amusements of innocent character
  • Appropriate food consumption2

A review study was done to understand lived experience of reducing caffeine consumption including specific techniques (what) and implementation strategies (how), harm and withdrawal symptoms (why). A classification system through an inductive and deductive approach was developed and applied to a large dataset derived from online sources. The findings of the studies are, a total of 112 internet sources were identified, containing 2,682 different strategies. The classification system identified 22 categories of Behaviour Change Techniques (BCT): 10 categories were directly aligned with a BCT, one was split into two categories (substance and behavioural substitution), six represented a cluster of BCT’s (e.g., withdrawal management and maintaining momentum) and four appeared to uniquely represent a consumer perspective (e.g., realisation of a problem). The most common techniques were substance substitution, seek knowledge and information, avoidance of caffeine and identify prompts for change. The most frequently perceived benefit was the stimulating effects of caffeine and a feeling of mental alertness. The most frequently cited harms were sleep problems including insomnia and concerns about dependence (or addiction) to caffeine. 16 categories of withdrawal symptoms were found. The most frequently endorsed symptom was headaches, followed by fatigue, exhaustion and low energy. The study concluded that a wide range of techniques were used by consumers when they attempt to reduce caffeine and they most frequently used approach of focus on substance and behavioural substitution.15

Table:1: Synopsis of the articles reviewed in comparison to Hahnemann’s writing

Serial Number Article Category Positive or negative association with Hahnemann’s writing
1. Haskell-Ramsay CF et al., 2018 Mind and Memory Positive association
2. Sane RM et al., 2019 Mind and Memory Positive association
3. Sartini M et al., 2019 Gastro-intestinal symptoms No association
4. Kane TD et al., 2020 Gastro-intestinal symptoms Negative association
5. Kondo K et al., 2021 Respiratory Symptoms Negative association
6. Alfaro TM et al., 2018 Respiratory Symptoms Negative association
7. Lopez DS et al., Sexual sphere No association
8. Adnan SM et al., 2020 Sexual sphere Positive association
9. Tesselaar E et al., 2017 Skin Positive association
10. Chau YP et al., 2020 Bone Mineral Density Positive association
11. Anderson JR et al., 2018 Sleep No association
12. O’Callaghan F et al., 2018 Sleep Positive association
13. Rodda S et al., 2020 Discontinuing the use of coffee Positive association

A total of 13 articles were reviewed along with Hahnemann’s writing which showed 8 modern study findings were in positive association with Hahnemann’s writing, 3 with negative association and 3 with no association. The review concludes that there is maximum positive association of Hahnemann’s writing with the findings of Modern scientific studies considered in this review which indicates the relevance of Hahnemann’s writing in today’s scientific world. There is need for more interventional studies to validate the findings of this review article.


  1. Nieber K. The impact of coffee on health. Planta medica. 2017 Nov;83(16):1256-63. https://www.thieme-connect.com/products/ejournals/html/10.1055/s-0043-115007
  2. Hahnemann S. “The Lesser Writings of Samuel Hahnemann” 14th impression Noida: B. Jain Publishers (P) ltd; 2019; 391-410
  3. Haskell-Ramsay CF, Jackson PA, Forster JS, Dodd FL, Bowerbank SL, Kennedy DO. The acute effects of caffeinated black coffee on cognition and mood in healthy young and older adults. Nutrients. 2018 Sep 30;10(10):1386. https://www.mdpi.com/2072-6643/10/10/1386
  4. Sane RM, Jadhav PR, Subhedar SN. The acute effects of decaffeinated versus caffeinated coffee on reaction time, mood and skeletal muscle strength. Journal of Basic and Clinical Physiology and Pharmacology. 2019 Sep 1;30(5). https://www.degruyter.com/document/doi/10.1515/jbcpp-2018-0119/html?lang=de
  5. Sartini M, Bragazzi NL, Spagnolo AM, Schinca E, Ottria G, Dupont C, Cristina ML. Coffee consumption and risk of colorectal cancer: A systematic review and meta-analysis of prospective studies. Nutrients. 2019 Mar 24;11(3):694. https://www.mdpi.com/2072-6643/11/3/694
  6. Kane TD, Tubog TD, Schmidt JR. The use of coffee to decrease the incidence of postoperative ileus: a systematic review and meta-analysis. Journal of PeriAnesthesia Nursing. 2020 Apr 1;35(2):171-https://www.sciencedirect.com/science/article/abs/pii/S108994721930365X
  7. Kondo K, Suzuki K, Washio M, Ohfuji S, Adachi S, Kan S, Imai S, Yoshimura K, Miyashita N, Fujisawa N, Maeda A. Association between coffee and green tea intake and pneumonia among the Japanese elderly: a case-control study. Scientific reports. 2021 Mar 10;11(1):1-8. https://www.nature.com/articles/s41598-021-84348-w
  8. Alfaro TM, Monteiro RA, Cunha RA, Cordeiro CR. Chronic coffee consumption and respiratory disease: A systematic review. The clinical respiratory journal. 2018 Mar;12(3):1283-94. https://onlinelibrary.wiley.com/doi/abs/10.1111/crj.12662
  9. Lopez DS, Liu L, Rimm EB, Tsilidis KK, de Oliveira Otto M, Wang R, Canfield S, Giovannucci E. Coffee intake and incidence of erectile dysfunction. American journal of epidemiology. 2018 May 1;187(5):951-9. https://academic.oup.com/aje/article/187/5/951/4093018
  10. Adnan SM, Farhana I, Park SJ, Rempoulakis P, Taylor PW. Caffeine as a promotor of sexual development in sterile Queensland fruit fly males. Scientific Reports. 2020 Sep 8;10(1):1-4. https://www.nature.com/articles/s41598-020-71671-x
  11. Tesselaar E, Dernroth DN, Farnebo S. Acute effects of coffee on skin blood flow and microvascular function. Microvascular Research. 2017 Nov 1;114:58-64. https://www.sciencedirect.com/science/article/abs/pii/S0026286217300973
  12. Chau YP, Au PC, Li GH, Sing CW, Cheng VK, Tan KC, Kung AW, Cheung CL. Serum metabolome of coffee consumption and its association with bone mineral density: the Hong Kong Osteoporosis Study. The Journal of Clinical Endocrinology & Metabolism. 2020 Mar;105(3):e619-27. https://academic.oup.com/jcem/article/105/3/e619/5637088
  13. Anderson JR, Hagerdorn PL, Gunstad J, Spitznagel MB. Using coffee to compensate for poor sleep: Impact on vigilance and implications for workplace performance. Applied ergonomics. 2018 Jul 1;70:142-https://www.sciencedirect.com/science/article/abs/pii/S0003687018300607
  14. O’Callaghan F, Muurlink O, Reid N. Effects of caffeine on sleep quality and daytime functioning. Risk management and healthcare policy. 2018;11:263. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6292246/
  15. Rodda S, Booth N, McKean J, Chung A, Park JJ, Ware P. Mechanisms for the reduction of caffeine consumption: What, how and why. Drug and Alcohol Dependence. 2020 Jul 1;212:108024 https://sci-hub.se/https://doi.org/10.1016/j.drugalcdep.2020.108024

Dr Meenu Priya A
PG Scholar, Department of Organon of Medicine with Homoeopathic philosophy, GHMC&H, Bengaluru

UGO: Dr Vijayalakshmi M. Angadi
Associate professor, Department of Organon of Medicine with Homoeopathic philosophy, GHMC&H, Bengaluru.

Be the first to comment

Leave a Reply

Your email address will not be published.