Effects of Caffeine and L-Theanine on Physical and Cognitive Performance in Trained Athletes

NCT07268573 | Completed

• 1 other identifier: 2025/337
• Study Type: interventional
• Target: 20
• Locations: 1 country
• Sites: 1

Brief Summary

The aim of this clinical trial is to examine how caffeine and L-theanine, taken alone or together, affect both physical and cognitive performance in healthy, trained athletes. The study aims to answer whether these commonly consumed dietary ingredients can enhance strength, endurance, and hand-eye coordination under controlled laboratory conditions. Researchers will compare four supplementation conditions: Caffeine (CAF) - 3 mg per kilogram of body weight L-Theanine (THE) - 200 mg Combined Caffeine and L-Theanine (COM) - same doses together Placebo (CON) - mannitol (inactive substance) Each participant will complete all four test sessions in a randomized, double-blind, crossover design, with at least 72 hours between sessions. Capsules will be taken 60 minutes before testing to allow time for absorption. During each session, participants will perform a series of physical and cognitive tasks, including maximal isometric strength tests, an intermittent endurance test, and a computerized eye-hand coordination task. The main hypothesis is that caffeine and L-theanine, alone or in combination, will improve strength and cognitive coordination compared with placebo. All participants are healthy competitive athletes between 18 and 30 years old. The study is conducted under standardized laboratory and indoor sports-hall conditions, with ethics approval obtained from the Sinop University Human Research Ethics Committee (Approval No. 2025/337).

Conditions

Cognitive Performance; Physical Performance Enhancement; Caffeine and L-theanine Interaction

Outcome Measures

Primary Outcomes (8)

• Total Distance Covered in the Yo-Yo Intermittent Endurance Test Level 1 (meters)

  Distance (m) completed during the Yo-Yo Intermittent Endurance Test Level 1 following standard protocol.

  60 minutes post-supplement ingestion.

• Peak Handgrip Force (kgf)

  Highest handgrip force obtained from three maximal voluntary contractions using a calibrated digital dynamometer.

  60 minutes post-supplement ingestion.

• Peak Back Extension Force (kgf)

  Highest value from three maximal voluntary contractions measured with a back strength dynamometer.

  60 minutes post-supplement ingestion.

• Peak Leg Extension Force (kgf)

  Highest value from three maximal voluntary contractions measured using a leg dynamometer.

  60 minutes post-supplement ingestion.

• Eye-Hand Coordination Accuracy (EHC-A)

  Accuracy percentage (%) obtained from the computerized eye-hand coordination test battery.

  60 minutes post-supplement ingestion.

• Eye-Hand Coordination Fast Speed Reaction Time (EHC-FS)

  Reaction time (milliseconds) during the fast-speed EHC trial.

  60 minutes post-supplement ingestion.

• Eye-Hand Coordination Slow Speed Reaction Time (EHC-SS)

  Reaction time (milliseconds) during the slow-speed EHC trial.

  60 minutes post-supplement ingestion.

• Eye-Hand Coordination Distance From Ball Center (EHC-DFBC)

  Mean deviation from target center measured during coordination task.

  60 minutes post-supplement ingestion.

Study Arms (4)

Caffeine Supplementation (CAF)

EXPERIMENTAL

Participants receive 3 mg of anhydrous caffeine per kilogram of body weight, encapsulated in gelatin capsules identical in appearance to other conditions. Capsules are ingested with water 60 minutes before testing.

Dietary Supplement: Caffeine

L-Theanine Supplementation (THE)

EXPERIMENTAL

Participants receive 200 mg of L-theanine (pure L-theanine powder, Orzax Pharmaceuticals, Istanbul, Turkey), encapsulated in gelatin capsules identical in appearance to other conditions. Capsules are ingested with water 60 minutes before testing.

Dietary Supplement: L-theanine

Combined Caffeine and L-Theanine (COM)

EXPERIMENTAL

Participants receive a combination of 3 mg/kg anhydrous caffeine and 200 mg L-theanine, encapsulated together in identical gelatin capsules. Capsules are taken 60 minutes before testing to assess potential synergistic effects on physical and cognitive performance.

Dietary Supplement: Combined Caffeine and L-Theanine

Placebo (CON)

PLACEBO COMPARATOR

Participants receive placebo capsules filled with mannitol, a non-nutritive sugar alcohol with no known ergogenic properties. Capsules are identical in size, color, texture, and weight to the active supplement conditions and are ingested 60 minutes before testing.

Dietary Supplement: Placebo

Interventions

Caffeine DIETARY_SUPPLEMENT

Participants receive 3 mg of anhydrous caffeine per kilogram of body weight, encapsulated in identical gelatin capsules (five in total). Capsules are taken orally with water 60 minutes before testing. The caffeine powder (98.5% purity, Oxford Vitality Health Co., UK) is administered once per experimental session, with at least 72 hours between conditions.

Caffeine Supplementation (CAF)

L-theanine DIETARY_SUPPLEMENT

Participants receive a single 200 mg dose of L-theanine (Orzax Pharmaceuticals, Istanbul, Turkey; active ingredient manufactured in Germany) encapsulated in identical gelatin capsules. The supplement is ingested orally with water 60 minutes before testing. All testing sessions are separated by at least 72 hours.

L-Theanine Supplementation (THE)

Combined Caffeine and L-Theanine DIETARY_SUPPLEMENT

Participants receive a combination of 3 mg/kg anhydrous caffeine and 200 mg L-theanine, encapsulated together in visually identical gelatin capsules. The mixture is taken orally with water 60 minutes before testing to assess potential synergistic effects on performance. Each participant completes all four supplementation conditions in randomized order, separated by ≥72 hours.

Combined Caffeine and L-Theanine (COM)

Placebo DIETARY_SUPPLEMENT

Participants receive placebo capsules filled with mannitol, a non-nutritive sugar alcohol with no known ergogenic or ergolytic effects. Capsules are identical in appearance, weight, and texture to the active supplement capsules and are taken orally with water 60 minutes before testing.

Placebo (CON)

Eligibility Criteria

• Age: 18 Years - 30 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Active participation in individual or team sports at a competitive level
• Age between \[insert range, e.g., 18-30\] years
• Absence of any known medical or metabolic disorder

You may not qualify if:

• History of cardiovascular, neurological, or musculoskeletal disorders within the past 12 months
• Known intolerance or hypersensitivity to caffeine or theanine
• Allergy to mannitol or other excipients used in capsule formulation
• Current use of prescription medications
• Physician-directed restriction of caffeine or theanine consumption.

Sponsors & Collaborators

• Ulaş Can YILDIRIM: lead

Study Sites (1)

Sinop University Facility

Sinop, Centarl, 57100, Turkey (Türkiye)

Location

Related Publications (1)

• Tuncer SY, Ozdenk S, Yildirim UC, Erkan D, Sari C, Gundem MC, Sar H, Yilmaz B, Karakulak I, Akca F. Acute effects of combined and isolated caffeine and theanine supplementation on physical and cognitive performance in competitive athletes: a randomized, double-blind, placebo-controlled crossover study. Front Nutr. 2026 Jan 26;12:1751673. doi: 10.3389/fnut.2025.1751673. eCollection 2025.

  PMID: 41668720 DERIVED

MeSH Terms

Interventions

Caffeine; theanine

Intervention Hierarchy (Ancestors)

Xanthines; Alkaloids; Heterocyclic Compounds; Purinones; Purines; Heterocyclic Compounds, 2-Ring; Heterocyclic Compounds, Fused-Ring

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: QUADRUPLE
• Who Masked: PARTICIPANT, CARE PROVIDER, INVESTIGATOR, OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Assoc. Prof.

Study Record Dates

• First Submitted: November 18, 2025
• First Posted: December 8, 2025
• Study Start: August 1, 2025
• Primary Completion: August 14, 2025
• Study Completion: August 14, 2025
• Last Updated: December 8, 2025

Record last verified: 2025-11

Data Sharing

• IPD Sharing: Will not share

Locations

TU (1)