PACAP-38 vs TB-500
Neuroprotective polypeptide with potent anti-inflammatory and cytoprotective properties discovered in 1989
A powerful fragment of thymosin beta-4 that acts like your body's repair signal—speeding up healing of muscles, tendons, and tissues by promoting cell migration and new blood vessel growth right where you need it most.
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
TB-500
2–2.5 mg
Frequency
PACAP-38
Once daily
TB-500
Twice weekly
Administration
PACAP-38
Intravenous infusion
TB-500
Subcutaneous injection
Cycle length
PACAP-38
Ongoing/indefinite
TB-500
4-6 weeks
Onset speed
PACAP-38
Moderate (1-2 weeks)
TB-500
Moderate (1-2 weeks)
Evidence level
PACAP-38
Strong human trials (Phase 3 or FDA approved)
TB-500
Moderate human trials (Phase 1-2)
Benefit ratings
Neuroprotection
Anti-Inflammatory
Migraine Research
Healing Speed
Tissue Repair
Anti-Scarring
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
TB-500
Molecular formula
C38H68N10O14
Molecular weight
889.01 g/mol
Half-life
2-3 days (systemic)
Bioavailability
High via subcutaneous injection (~100%)
CAS number
885340-08-9
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.
TB-500
Subcutaneous
2-2.5 mg
Twice weekly · Loading phase, 4-6 weeks
Research peptide with no human trials of the fragment; [9] loading doses used in practice [6].
2-2.5 mg
Once weekly · Maintenance after loading
Maintenance dose used in practice following the loading phase [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.
TB-500
Athletes Recovering from Muscle Injuries
If you've pulled a hamstring, strained your back, or torn a muscle, TB-500 helps accelerate the healing process by promoting cell migration to the injury site and supporting new blood vessel growth. It's especially useful for injuries that just won't seem to fully heal [1][5].
Tendon and Ligament Problems
Tendons and ligaments are notoriously slow healers because they have poor blood supply. TB-500 promotes angiogenesis (new blood vessel formation) and helps repair these stubborn connective tissue injuries—think Achilles tendonitis, tennis elbow, or rotator cuff issues [5].
Post-Surgical Recovery
After surgery, your body needs to repair a lot of tissue quickly. TB-500 supports wound healing, reduces inflammation, and may help minimize scar tissue formation. Some protocols use it alongside traditional recovery to potentially speed up the healing timeline [1][4].
Chronic Inflammation and Slow Healers
Some people just heal slowly—whether due to age, diabetes, or other factors. TB-500 helps regulate the inflammatory response and promotes the cellular processes needed for tissue repair. It essentially tells your body to focus healing resources where they're needed most [1].
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
TB-500
Common
- Injection site redness
- Mild fatigue or lethargy
- Mild headache
- Slight flushing
Uncommon
- Head rush or lightheadedness
- Temporary nausea
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
TB-500
Evidence level
Moderate human trials (Phase 1-2)
FDA status
Research compound
Safety overview
TB-500 has shown a good safety profile across preclinical studies and limited human research. It's a fragment of thymosin beta-4, a naturally occurring protein in your body involved in healing. Most side effects are mild and transient, primarily injection site reactions. However, large-scale clinical trials are still needed to fully establish its safety profile in humans [1].
Contraindications
- Pregnancy or planning to become pregnant
- Currently breastfeeding
- Active cancer or history of cancer
- Known allergy to peptide components
- Children and adolescents
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 TB-500 if...
- Accelerating injury recovery
- Tendon and ligament healing
- Reducing chronic inflammation
- Post-surgical recovery support