What you carry at this position in your DNA and what research says about it.
Caffeine Sensitivity: 6/10 evidence, 22 publications.
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Sample genotype (not yours): T/T
Higher Risk of Caffeine-Induced Anxiety
Carrying two copies of the T allele is strongly linked to feeling highly anxious or jittery after consuming moderate amounts of caffeine. However, this genotype may offer some protection against caffeine-induced sleep disruption.
What this genotype means: Increased anxiety after moderate caffeine; Poorer response to methotrexate; Lower risk of caffeine-induced insomnia.
Sample genotype (not yours): C/C
Lower Anxiety but Higher Insomnia Risk
Carrying two copies of the C allele protects against caffeine-induced anxiety but increases the likelihood of sleep disruption and insomnia. This represents a classic genetic trade-off between mood and sleep.
What this genotype means: Lower risk of caffeine-induced anxiety; Higher risk of insomnia and sleep disruption; Typical response to methotrexate.
Sample genotype (not yours): T/C
Typical Response to Caffeine
Carrying one copy of each allele typically results in a moderate, average sensitivity to caffeine. There is also a potential for a slightly reduced response to methotrexate treatment.
What this genotype means: Typical caffeine tolerance; Slightly poorer response to methotrexate.
Gene function and biological role
Gene Function: The ADORA2A gene encodes the adenosine A2a receptor, a critical protein in the brain that detects adenosine to promote sleep and relaxation [1]. Adenosine buildup throughout the day signals the body that it is time to rest [1]. Caffeine acts as a stimulant primarily by blocking these adenosine receptors, preventing them from receiving the calming signals [2]. Because ADORA2A is highly expressed in dopamine-rich brain regions, it also plays a key role in regulating mood, anxiety, and stress responses [3]. Variations in this gene can alter how strongly caffeine blocks these receptors, directly influencing an individual's susceptibility to caffeine-induced jitters or sleep disturbances [4].
Variant Impact: Located within the ADORA2A gene, rs5751876 is a synonymous change that does not alter the final amino acid sequence of the receptor protein but can still affect how the gene is expressed or translated [5]. Also known as 1976C>T, this specific genetic variation is one of the most widely studied markers for individual differences in caffeine response [2]. It is in tight linkage disequilibrium with other functional variants that modify adenosine receptor binding in the human brain [5]. Depending on the inherited alleles, this variant can significantly shift the balance between caffeine's desirable alerting effects and its unpleasant side effects like panic, jitteriness, or insomnia [4].
Read on the Caffeine Jitters page
Key Insight: Your brain's sensitivity to caffeine is heavily regulated by adenosine receptors, meaning coffee jitters and caffeine-induced insomnia are deeply rooted in your genetic makeup rather than just lifestyle habits.
Location: ADORA2A. Chromosome 22 · 22q11.23 · 24.4 Mb
Estimated prevalence by population
Global 24.3%; European 15.4%; African 40.7%; East Asian 25.6%; South Asian 42.5%; Americas 19.2%; Ashkenazi 16.6%; Finnish 18.3%; Middle Eastern 24.7%; Amish 15.9%.
Estimated TT genotype frequency.
Global 47.6%; European 47.7%; African 46.2%; East Asian 50.0%; South Asian 45.4%; Americas 49.2%; Ashkenazi 48.3%; Finnish 49.0%; Middle Eastern 50.0%; Amish 48.0%.
Estimated TC genotype frequency.
Global 28.2%; European 36.8%; African 13.1%; East Asian 24.4%; South Asian 12.1%; Americas 31.5%; Ashkenazi 35.1%; Finnish 32.7%; Middle Eastern 25.3%; Amish 36.1%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Nutrition & Metabolism
Caffeine & Stimulant Metabolism
Caffeine-Induced Anxiety. Evidence: 6/10. Source: PMID 12825092. Increased Anxiety.
Neurology & Mental Health
Sleep & Circadian Rhythm
Insomnia. Evidence: 6/10. Source: PMID 17329997. Lower Insomnia Risk.
Anxiety & Stress Disorders
Panic Disorder. Evidence: 3/10. Source: PMID 20334879. Increased Risk.
Pharmacogenomics
Immunosuppressant & Biologic Response
Methotrexate Response. Evidence: 5/10. Source: PMID 19902562. Poorer Response.
Showing effects for C/C genotype
Caffeine-Induced Anxiety. Evidence: 6/10. Source: PMID 12825092. Lower Anxiety.
Insomnia. Evidence: 6/10. Source: PMID 17329997. Higher Insomnia Risk.
Panic Disorder. Evidence: 3/10. Source: PMID 20334879. Typical Risk.
Methotrexate Response. Evidence: 5/10. Source: PMID 19902562. Typical Response.
Showing effects for T/C genotype
Caffeine-Induced Anxiety. Evidence: 6/10. Source: PMID 12825092. Typical.
Insomnia. Evidence: 6/10. Source: PMID 17329997. Typical.
Panic Disorder. Evidence: 3/10. Source: PMID 20334879. Slightly Increased.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Experiencing acute anxiety, panic, or physical jitters after moderate caffeine consumption is highly common for those with the T/T genotype [1]. This response occurs because the T/T genotype alters adenosine receptor sensitivity, making the brain's stress pathways more reactive when caffeine blocks adenosine [2]. Interestingly, while caffeine is more likely to trigger anxiety in T/T carriers, some studies suggest they may actually experience less sleep disruption from low caffeine intake compared to C/C carriers [3]. Beyond caffeine, the T/T genotype has also been associated with a poorer response to methotrexate therapy in rheumatoid arthritis patients [4]. Managing caffeine intake by opting for low-dose alternatives like green tea can help mitigate these anxious side effects.
Increased anxiety after moderate caffeine; Poorer response to methotrexate; Lower risk of caffeine-induced insomnia.
Sample genotype: CC (Homozygous)
Protection against the acute anxiety and jitteriness that caffeine triggers in others is a key feature of the C/C genotype [1]. However, this benefit comes with a significant trade-off, as C/C carriers are much more sensitive to caffeine's sleep-disrupting effects, showing a higher likelihood of insomnia and reduced sleep quality even with moderate consumption [2]. This sensitivity is driven by how the C/C genotype influences adenosine receptors, which are crucial for regulating the sleep-wake cycle [3]. Consequently, while a C/C individual can drink coffee without feeling anxious, consuming it too late in the day is highly likely to interfere with their ability to fall asleep [4]. They also tend to have a typical, standard response to methotrexate therapy [5].
Lower risk of caffeine-induced anxiety; Higher risk of insomnia and sleep disruption; Typical response to methotrexate.
Sample genotype: TC (Heterozygous)
Representing an intermediate genetic profile, the T/C genotype results in a typical or average sensitivity to caffeine's stimulating and anxiety-inducing effects. Unlike T/T homozygotes, individuals with the T/C genotype do not usually experience severe, acute anxiety or panic from moderate caffeine consumption [1]. Similarly, they do not exhibit the heightened sleep sensitivity or insomnia risk frequently observed in C/C homozygotes [2]. However, in the context of autoimmune treatments, some research indicates that T/C carriers may have a poorer clinical response to methotrexate, similar to T/T carriers [3]. For most daily activities, this genotype allows for a standard tolerance to coffee and tea without extreme adverse reactions.
Typical caffeine tolerance; Slightly poorer response to methotrexate.
Variants with shared genetic architecture
rs3761422 · ADORA2A Gene · Chr 22 · Caffeine Jitters and Sleep
rs2298383 · ADORA2A-AS1 Gene · Chr 22 · Caffeine Sensitivity
rs324981 · NPSR1 Gene · Chr 7 · Anxiety and Sleep Duration
Association between A2a receptor gene polymorphisms and caffeine-induced anxiety.
Association between ADORA2A and DRD2 polymorphisms and caffeine-induced anxiety.
Genotyping sleep disorders patients.
Content updated August 2026.
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