Caffeine vs Glycine
Performance vs Sleep · evidence-backed comparison
- • Caffeine has the stronger evidence base (strong (multiple rcts / meta-analyses)).
- • Caffeine has the broader effect profile across the 9 effect categories.
- • Caffeine is cheaper per serving ($0.05 vs $0.10).
- • Glycine has a slightly cleaner safety profile.
Side-by-side traits
| Trait | Caffeine | Glycine |
|---|---|---|
Category | Performance | Sleep |
Active compound | 1,3,7-trimethylxanthine | Glycine |
Form available | Powder, Capsule, Tablet | Powder, Capsule |
Source | synthetic | synthetic |
Typical dose | 100–300 mg | 3 g before bed |
Dose range | 100–300 mg | 3–5 g |
Loading protocol | — | — |
Best taken with | water | water, 30 min before bed |
Best time of day | morning | evening |
Bioavailability How efficiently the body absorbs and utilizes the compound. | Very High (5/5) | Very High (5/5) |
Onset time | Acute: 30–60 min | Acute: 30–60 min |
Half-life | 5–6 hours (plasma) | ~1 hour |
Evidence level Quality and quantity of human research. | Strong (multiple RCTs / meta-analyses) | Moderate (some RCTs) |
Overall effect Subjective effect magnitude. | High (4/5) | Low (2/5) |
Muscle / strength | Low (2/5) | Low (2/5) |
Physical energy | Very High (5/5) | Very Low (1/5) |
Focus / cognition | Very High (5/5) | Low (2/5) |
Mood / stress | High (4/5) | Moderate (3/5) |
Sleep quality | Very Low (1/5) | High (4/5) |
Immunity | Low (2/5) | Very Low (1/5) |
Recovery Post-exercise recovery support. | Very Low (1/5) | Low (2/5) |
Longevity / healthspan | Moderate (3/5) | Moderate (3/5) |
Safety rating 5 = exceptionally well-tolerated; 1 = significant risk profile. | High (4/5) | Very High (5/5) |
Price per serving Approximate USD per typical daily dose. | $0.05 | $0.10 |
Vegan friendly | Yes | Yes |
Gluten free | Yes | Yes |
3rd-party tested | Yes | Yes |
About Caffeine
The most effective legal performance booster. Boosts strength, endurance, focus, and pain tolerance — but tolerance builds within weeks.
About Glycine
Sweet-tasting amino that lowers core body temperature for deeper sleep. Cheap, well-tolerated, and especially useful with magnesium glycinate.
Vetted brands, third-party testing, ships worldwide.
Vetted brands, third-party testing, ships worldwide.
Caffeine safety
Common side effects:
- • Jitters
- • Insomnia
- • Increased heart rate
- • GI upset
Avoid if:
- • Anxiety disorders
- • Heart arrhythmias
- • Pregnancy (limit 200 mg/day)
Drug interactions:
- • MAOIs
- • Theophylline
- • Birth control
Glycine safety
Common side effects:
- • Generally none
Avoid if:
- • Clozapine therapy
Drug interactions:
- • Clozapine
Common uses
- • Energy
- • Pre-workout
- • Focus
- • Fat loss
Stacks well with: L-Theanine, Creatine Monohydrate, Beta-Alanine
Common uses
- • Deep sleep
- • Sleep quality
- • Collagen synthesis
Stacks well with: Magnesium Glycinate, Melatonin
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Medical disclaimer
SupplementDuel is for educational purposes only and is not medical advice. Consult a physician before starting, stopping, or combining supplements — especially if you are pregnant, breastfeeding, take prescription medication, or have a chronic condition.