PACAP-38 vs Thymosin Beta-4
Neuroprotective polypeptide with potent anti-inflammatory and cytoprotective properties discovered in 1989
The body's natural healing peptide that accelerates tissue repair and reduces inflammation
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
PACAP-38
10–10 pmol/kg/min
Thymosin Beta-4
2–5 mg
Frequency
PACAP-38
Once daily
Thymosin Beta-4
Twice weekly
Administration
PACAP-38
Intravenous infusion
Thymosin Beta-4
Subcutaneous injection
Cycle length
PACAP-38
Ongoing/indefinite
Thymosin Beta-4
8-12 weeks
Onset speed
PACAP-38
Moderate (1-2 weeks)
Thymosin Beta-4
Moderate (1-2 weeks)
Evidence level
PACAP-38
Strong human trials (Phase 3 or FDA approved)
Thymosin Beta-4
Moderate human trials (Phase 1-2)
Benefit ratings
Neuroprotection
Anti-Inflammatory
Migraine Research
Wound Healing
Inflammation Reduction
Tissue Regeneration
Compound specifications
PACAP-38
Molecular formula
C203H331N63O53S
Molecular weight
~4534 Da
Half-life
Very short plasma half-life (minutes); rapid enzymatic degradation
Bioavailability
IV: systemic; Intranasal: direct CNS access bypassing BBB; poor oral bioavailability
CAS number
137061-48-4
Thymosin Beta-4
Molecular formula
C212H350N56O78S
Molecular weight
4963
Half-life
Dose-dependent (increases with higher doses)
Bioavailability
100% (subcutaneous and intravenous)
CAS number
77591-33-4
Dosing compared
PACAP-38
Intravenous
10 pmol/kg/min
Continuous infusion · 20-minute single infusion
Standardized human experimental-medicine provocation dose; 10 pmol/kg/min over 20 min was selected as the optimal/maximum tolerated rate after dose-finding (5-20 pmol/kg/min) and is reproduced across headache-model trials [6][7][8]. Used as a research provocation agent, not an approved therapeutic.
Thymosin Beta-4
Subcutaneous injection
2-5 mg (community injectable practice for 'TB-500')
Once or twice weekly · 4-6 week loading phase, then weekly maintenance
Documented community/research-practice injectable dosing for tissue repair; thymosin beta-4 has ~100% bioavailability by the subcutaneous route [1]. Not an FDA-approved use.
Topical ophthalmic (eye drops)
0.1% (1 mg/mL) RGN-259 solution, 1 drop
Several times daily (e.g. up to 5x/day) · 4 weeks
0.1% RGN-259 ophthalmic solution used in phase III neurotrophic keratopathy and dry-eye trials, applied as eye drops several times daily for ~4 weeks [5].
Intravenous injection
450-1200 mg
IV push daily for the first 3 days, then weekly · Total of 7 doses over ~5 weeks
Doses studied in the RGN-352 acute myocardial infarction clinical program, given IV after PCI [6].
Best suited for
PACAP-38
Neuroprotection research
PACAP-38 is particularly well-suited for individuals focused on neuroprotection research. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Stroke and traumatic brain injury investigation
PACAP-38 is particularly well-suited for individuals focused on stroke and traumatic brain injury investigation. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Migraine pathophysiology studies
PACAP-38 is particularly well-suited for individuals focused on migraine pathophysiology studies. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Anti-inflammatory mechanism research
PACAP-38 is particularly well-suited for individuals focused on anti-inflammatory mechanism research. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Thymosin Beta-4
Post-Surgery Recovery
Accelerates healing of surgical wounds and reduces post-operative inflammation and scarring
Chronic Wound Management
Helps pressure ulcers, venous stasis ulcers, and other slow-healing wounds progress faster
Tissue Regeneration
Supports repair of damaged tissues from injury, burns, or degenerative conditions
Side effects
PACAP-38
Common
- Flushing
- Tachycardia
- Gastrointestinal Effects
- Transient Warmth Sensation
Uncommon
- Headache and Migraine Triggering
- Hypotension
Serious
- Systemic Hypotension and Cardiovascular Effects
- Systemic Inflammatory Activation
Thymosin Beta-4
Common
- Injection site redness
- Injection site swelling
Uncommon
- Temporary mild headache
- Mild bruising at injection site
- Transient fatigue
Serious
- Allergic reaction
Safety & evidence
PACAP-38
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
Research compound
Safety overview
PACAP-38 shows good tolerability in Phase II trials for migraine and pain conditions with minimal serious adverse events at IV doses of 2-6 mcg/kg. Primary side effects are transient flushing and headache (10-15% of subjects), likely related to vasodilation. Cardiovascular effects include mild heart rate increase and blood pressure changes, monitored in clinical settings. No carcinogenicity or teratogenicity in animal models; limited long-term safety data in humans.
Contraindications
- Active migraine or headache disorder (PACAP-38 is a potent migraine trigger)
- Uncontrolled hypotension or cardiovascular instability
- Not approved for clinical use outside research settings
- Insufficient data for pregnancy and lactation safety
Thymosin Beta-4
Evidence level
Moderate human trials (Phase 1-2)
FDA status
Research compound
Safety overview
Thymosin Beta-4 is a naturally occurring peptide found in all cells and body fluids in the human body. Clinical trials have demonstrated excellent safety even at very high doses. IV studies showed doses up to 1260 mg were well tolerated with no serious adverse events.
Contraindications
- Active systemic infections
- Severe immunosuppression
- Hypersensitivity to thymosin or any component
- Pregnancy (insufficient safety data)
Which is right for you?
Choose PACAP-38 if...
- Neuroprotection research
- Stroke and traumatic brain injury investigation
- Migraine pathophysiology studies
- Anti-inflammatory mechanism research
Choose Thymosin Beta-4 if...
- Recovering from injuries or surgery
- Improving wound healing speed
- Reducing inflammation
- Minimizing scar formation