What you carry at this position in your DNA and what research says about it.
Stress and Mood Regulation: 6/10 evidence, 51 publications.
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Sample genotype (not yours): T/T
Better Antidepressant Response and Lower Serotonin Levels
This genotype is linked to lower baseline serotonin levels and slightly lower life satisfaction, but predicts a better therapeutic response to venlafaxine. It also carries a typical risk for citalopram side effects.
What this genotype means: Lower baseline serotonin transporter expression; Better therapeutic response to venlafaxine; Typical risk of citalopram side effects.
Sample genotype (not yours): C/C
Higher Life Satisfaction and Increased Medication Sensitivity
This genotype is associated with higher life satisfaction, lower pain sensitivity, and greater stress resilience, but carries an increased risk of citalopram side effects.
What this genotype means: Higher baseline life satisfaction and stress resilience; Lower sensitivity to physical pain; Increased risk of citalopram side effects.
Sample genotype (not yours): T/C
Typical Serotonin Activity with Elevated Side Effect Risk
This genotype represents an intermediate genetic profile with typical baseline serotonin levels, but carries an increased likelihood of side effects when taking citalopram.
What this genotype means: Intermediate serotonin transporter expression; Increased likelihood of citalopram side effects; Typical baseline life satisfaction.
Gene function and biological role
Gene Function: The SLC6A4 gene encodes the serotonin transporter, a crucial protein responsible for recycling serotonin from the synaptic cleft back into neurons. This transport process directly regulates the intensity and duration of serotonin signaling in brain networks that control mood, stress responses, and emotional processing. Variations in this gene are among the most extensively researched factors in psychiatric genetics and behavioral neuroscience. Because the transporter is the primary target for selective serotonin reuptake inhibitors (SSRIs), SLC6A4 is also a major focus of pharmacogenomic research.
Variant Impact: The rs25531 variant is a single nucleotide change located within the promoter region of the serotonin transporter gene. This nucleotide substitution alters the transcriptional efficiency of the promoter, directly modulating how much serotonin transporter protein is produced. It is frequently studied in tandem with the nearby 5-HTTLPR insertion/deletion polymorphism, as the two variations jointly shape overall serotonin system activity. The variant has been shown to influence emotional resilience, pain perception, and individual responses to common psychiatric medications.
Key Insight: This variant acts as a functional dial on the famous 5-HTTLPR 'happiness gene' region, modifying how strongly the serotonin transporter is expressed in the brain.
Location: SLC6A4. Chromosome 17 · 17q11.2 · 30.2 Mb
Estimated prevalence by population
Global 65.5%; European 75.9%; African 49.9%; East Asian 46.2%; South Asian 50.2%; Americas 67.3%; Ashkenazi 83.7%; Finnish 65.3%; Middle Eastern 81.0%; Amish 78.3%.
Estimated TT genotype frequency.
Global 30.1%; European 22.5%; African 41.5%; East Asian 43.6%; South Asian 41.3%; Americas 29.4%; Ashkenazi 15.6%; Finnish 31.0%; Middle Eastern 18.0%; Amish 20.4%.
Estimated TC genotype frequency.
Global 4.4%; European 1.7%; African 8.6%; East Asian 10.3%; South Asian 8.5%; Americas 3.2%; Ashkenazi 0.7%; Finnish 3.7%; Middle Eastern 1.0%; Amish 1.3%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Neurology & Mental Health
Behavioral & Personality Traits
Life Satisfaction. Evidence: 3/10. Source: PMID 23021380. Slightly Lower.
Organ Systems
Chronic Pain
Pain Sensitivity. Evidence: 3/10. Source: PMID 22271509. Typical.
Pharmacogenomics
Antidepressant & Psychiatric Drug Response
Venlafaxine Response. Evidence: 5/10. Source: PMID 22907732. Stronger Response.
Citalopram Side Effects. Evidence: 5/10. Source: PMID 19996755. Typical Risk.
Cardiovascular & Metabolic
Lipids & Cholesterol
Small LDL Particle Ratio. Evidence: 6/10. Source: PMID 41044249. Typical.
Showing effects for C/C genotype
Life Satisfaction. Evidence: 3/10. Source: PMID 23021380. Slightly Higher.
Pain Sensitivity. Evidence: 3/10. Source: PMID 22271509. Lower Sensitivity.
Venlafaxine Response. Evidence: 5/10. Source: PMID 22907732. Typical.
Citalopram Side Effects. Evidence: 5/10. Source: PMID 19996755. Increased Risk.
Small LDL Particle Ratio. Evidence: 6/10. Source: PMID 41044249. Higher Ratio.
Showing effects for T/C genotype
Life Satisfaction. Evidence: 3/10. Source: PMID 23021380. Typical.
Small LDL Particle Ratio. Evidence: 6/10. Source: PMID 41044249. Slightly Higher.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Lower levels of baseline serotonin transporter activity are characteristic of this genotype, which corresponds to the short form of the 5-HTTLPR region. Research suggests that individuals with this genetic profile may experience slightly lower overall life satisfaction and may benefit from stronger social and maternal support systems during development. However, from a pharmacogenomic standpoint, this genotype is associated with a significantly better response to the antidepressant venlafaxine. Additionally, it does not carry the elevated risk of citalopram-induced side effects seen in other genotypes. Understanding these patterns helps researchers map how genetic variations influence both baseline emotional traits and clinical treatment paths.
Lower baseline serotonin transporter expression; Better therapeutic response to venlafaxine; Typical risk of citalopram side effects.
Sample genotype: CC (Homozygous)
Higher baseline serotonin transporter expression is associated with this genotype, which corresponds to the long form of the 5-HTTLPR region. Population studies indicate that individuals with this profile report higher overall life satisfaction and demonstrate greater emotional resilience to stress. Clinical research also links this genetic variation to lower physical pain sensitivity. On the other hand, pharmacogenomic data indicates an increased likelihood of experiencing side effects when taking citalopram. Furthermore, genetic association studies have connected this profile to an elevated ratio of triglycerides to total lipids in small LDL particles.
Higher baseline life satisfaction and stress resilience; Lower sensitivity to physical pain; Increased risk of citalopram side effects.
Sample genotype: TC (Heterozygous)
An intermediate level of serotonin transporter expression is typical for this heterozygous profile. Baseline emotional resilience and life satisfaction generally align with population averages, showing no strong positive or negative deviations. In medical contexts, however, clinical studies have noted an increased likelihood of experiencing side effects when prescribed the antidepressant citalopram. There is also a slightly higher ratio of triglycerides to total lipids in small LDL particles compared to the major genotype. These findings highlight how heterozygous variations can introduce specific drug sensitivities even when baseline emotional traits remain typical.
Intermediate serotonin transporter expression; Increased likelihood of citalopram side effects; Typical baseline life satisfaction.
Variants with shared genetic architecture
rs2020942 · SLC6A4 Gene · Chr 17 · Body Fat and BMI
rs6354 · SLC6A4 Gene · Chr 17 · Serotonin and Mood
rs1042173 · SLC6A4 Gene · Chr 17 · Alcohol and Pain Sensitivity
Content updated August 2026.
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