L-Arginine vs L-Tryptophan
Amino Acid vs Sleep · evidence-backed comparison
- • L-Tryptophan has the stronger evidence base (moderate (some rcts)).
- • L-Tryptophan has the broader effect profile across the 9 effect categories.
- • L-Tryptophan has higher bioavailability (better absorption).
Side-by-side traits
| Trait | L-Arginine | L-Tryptophan |
|---|---|---|
Category | Amino Acid | Sleep |
Active compound | L-arginine | L-tryptophan |
Form available | Powder, Capsule | Capsule, Powder |
Source | microbial | microbial |
Typical dose | 3–6 g daily (acute) | 500–1500 mg |
Dose range | 3–6 g | 500–1500 mg |
Loading protocol | — | — |
Best taken with | empty stomach | carbs (improves CNS uptake), empty stomach |
Best time of day | pre-workout | evening |
Bioavailability How efficiently the body absorbs and utilizes the compound. | Low (2/5) | Moderate (3/5) |
Onset time | Acute: 60 min | Acute: 60 min |
Half-life | ~1 hour | ~2 hours |
Evidence level Quality and quantity of human research. | Limited (small studies) | Moderate (some RCTs) |
Overall effect Subjective effect magnitude. | Low (2/5) | Moderate (3/5) |
Muscle / strength | Low (2/5) | Very Low (1/5) |
Physical energy | Moderate (3/5) | Very Low (1/5) |
Focus / cognition | Very Low (1/5) | Very Low (1/5) |
Mood / stress | Very Low (1/5) | High (4/5) |
Sleep quality | Very Low (1/5) | High (4/5) |
Immunity | Low (2/5) | Very Low (1/5) |
Recovery Post-exercise recovery support. | Low (2/5) | Very Low (1/5) |
Longevity / healthspan | Low (2/5) | Very Low (1/5) |
Safety rating 5 = exceptionally well-tolerated; 1 = significant risk profile. | High (4/5) | High (4/5) |
Price per serving Approximate USD per typical daily dose. | $0.35 | $0.35 |
Vegan friendly | Yes | Yes |
Gluten free | Yes | Yes |
3rd-party tested | Yes | Yes |
About L-Arginine
Nitric oxide precursor — but most arginine is broken down in the gut. L-citrulline raises blood arginine more reliably for pumps.
About L-Tryptophan
Serotonin and melatonin precursor. Generally safer than 5-HTP for daily use, with strong sleep-onset and mood support.
Vetted brands, third-party testing, ships worldwide.
Vetted brands, third-party testing, ships worldwide.
L-Arginine safety
Common side effects:
- • GI upset
- • Diarrhea (high doses)
Avoid if:
- • Recent heart attack
- • Herpes flare-ups
Drug interactions:
- • Sildenafil, blood pressure meds
L-Tryptophan safety
Common side effects:
- • Drowsiness
- • GI upset
- • Dry mouth
Avoid if:
- • SSRI use (serotonin syndrome)
- • Liver disease
Drug interactions:
- • SSRIs
- • MAOIs
- • Sedatives
Common uses
- • Pump
- • Erectile function
- • Blood flow
Stacks well with: L-Citrulline
Common uses
- • Sleep onset
- • Mood
- • Carb cravings
Stacks well with: Magnesium Glycinate
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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.