Comparison
Low-Dose Naltrexone vs PT-141
Side-by-side of Low-Dose Naltrexone and PT-141. Every row below is pulled from the compound schema and will update as our data grows. For deeper reads, follow through to each compound page.
Low-Dose Naltrexone
Low dose naltrexone at 1.5 to 4.5 mg, one-tenth the 50 mg addiction dose. Compounded Rx. Small trials in fibromyalgia, Crohn's, Hashimoto's.
PT-141
PT-141 peptide (bremelanotide, Vyleesi): MC4R agonist for libido and erectile dysfunction. 1.75 mg subcutaneous, 30 to 60 min onset, 2 to 4 h half-life.
Effects at a glance
Low-Dose Naltrexone
- •Off-label use at 1.5 to 4.5 mg, roughly one-tenth the FDA-approved 50 mg addiction-treatment dose
- •Proposed mechanisms include brief opioid receptor blockade triggering rebound endogenous opioid release, plus TLR4 antagonism
- •Compounded prescription only; insurance rarely covers; cash prices 20 to 80 USD per month
- •Younger 2013 reported ~30% pain reduction in fibromyalgia at 4.5 mg in a small crossover trial
- •Smith 2011 reported endoscopic improvement in active Crohn's disease (n=40 placebo-controlled)
- •Vivid dreams affect 20 to 40% in first 2 weeks; manageable by switching to morning dosing
PT-141
- •Cyclic 7-amino-acid synthetic peptide and melanocortin receptor agonist (MC4R-preferring)
- •FDA approved in 2019 as Vyleesi for hypoactive sexual desire disorder in pre-menopausal women
- •Acts centrally on hypothalamic sexual-desire circuits rather than peripherally on vasculature
- •On-demand dosing: subcutaneous 1.75 mg approximately 45 minutes before sexual activity
- •Common adverse effects: nausea (~40%), flushing, headache, injection-site reactions, hyperpigmentation
- •Off-label male ED use is documented but not FDA approved; mechanism is distinct from PDE5 inhibitors
Side-by-side
| Attribute | Low-Dose Naltrexone | PT-141 |
|---|---|---|
| Category | pharmaceutical | peptide |
| Also known as | LDN, naltrexone (low dose) | Bremelanotide, Vyleesi |
| Half-life (hr) ↗ | 4 | 2.7 |
| Typical dose (mg) ↗ | 4.5 | 1.75 |
| Dosing frequency | once daily, typically at bedtime | as needed (max once per 24 hours, max 8 per month) |
| Routes | oral | subcutaneous |
| Onset (hr) | 1 | 0.75 |
| Peak (hr) | 1.5 | 1.5 |
| Molecular weight | 341.4 | 1025.18 |
| Molecular formula | C20H23NO4 | C50H68N14O10 |
| Mechanism | Brief mu-opioid receptor antagonism proposed to trigger compensatory upregulation of endogenous opioids; secondary TLR4 antagonism on microglia and immune cells contributes to anti-inflammatory effect. | Synthetic agonist of melanocortin receptors with preference for MC4R, expressed in hypothalamic and limbic circuits regulating sexual motivation. Engages central pathways distinct from peripheral PDE5-mediated vasodilation. |
| Legal status | Off-label compounded prescription (naltrexone is FDA approved for opioid and alcohol use disorder at 50 mg) | Prescription only as Vyleesi; FDA-approved 2019 for HSDD in pre-menopausal women. Compounded versions sold off-label for male sexual function are research-use-only grey market. |
| WADA status | allowed | allowed |
| DEA / Rx | Rx only (not a controlled substance) | Rx only (not a controlled substance) for the FDA-approved Vyleesi formulation |
| Pregnancy | Insufficient data; not routinely recommended | Not recommended; contraindicated during pregnancy per Vyleesi label |
| CAS | 16590-41-3 | 189691-06-3 |
| PubChem CID | 5360515 | 9941379 |
| Wikidata | Q426444 | Q422059 |
Safety profile
Low-Dose Naltrexone
Common side effects
- vivid dreams
- sleep disruption
- headache
- mild GI upset
- fatigue (early)
Contraindications
- concurrent opioid use
- acute hepatitis or liver failure
- opioid dependence
- pregnancy (insufficient data)
Interactions
- opioid analgesics (oxycodone, morphine, codeine): blocks analgesic effect; precipitates withdrawal in dependent users(major)
- tramadol: blocks opioid component of analgesia(major)
- thyroid hormone replacement: may alter dose requirements after immune modulation; monitor TSH(minor)
PT-141
Common side effects
- nausea (~40%)
- flushing
- headache
- injection-site reactions
- hyperpigmentation (focal, gums, face, breasts)
- transient blood pressure increase (~6 mmHg systolic)
Contraindications
- uncontrolled hypertension
- established cardiovascular disease
- pregnancy
- naltrexone co-administration (reduces opioid efficacy due to MC receptor crosstalk)
Interactions
- naltrexone (oral): bremelanotide reduces oral naltrexone exposure significantly; avoid co-administration(major)
- antihypertensives: transient BP rise after bremelanotide can offset BP control(moderate)
- PDE5 inhibitors (sildenafil, tadalafil): no documented adverse interaction; mechanisms are non-overlapping(minor)
Which Should You Take?
Low-Dose Naltrexone comes out ahead for most readers on the criteria we weight: 2 catalogued goals, prescription-only, oral dosing, with a Tier-A outcome catalogued. PT-141 is the right call when one of the conditionals below applies.
- → If your priority is immune support, pick Low-Dose Naltrexone.
- → If your priority is pain modulation, pick Low-Dose Naltrexone.
- → If your priority is sexual function, pick PT-141.
- → If your priority is libido, pick PT-141.
Edge case: If you cannot self-administer injections, Low-Dose Naltrexone is the only oral option in this pair.
Default choice: Low-Dose Naltrexone. Wider use case, a Tier-A evidence outcome catalogued, and broader goal coverage. Reach for PT-141 only if your priority sits squarely in the goals it owns above.
This verdict is generated from each compound's schema (goals, legal status, evidence outcomes, dosing route). It updates automatically as our compound data evolves; the deeper read sits on each individual compound page.
Common questions
What is the difference between Low-Dose Naltrexone and PT-141?
Low-Dose Naltrexone and PT-141 differ in category (pharmaceutical vs peptide), mechanism, and typical dosing. See the side-by-side table for full details.
Which has a longer half-life, Low-Dose Naltrexone or PT-141?
Low-Dose Naltrexone half-life is 4 hours; PT-141 half-life is 2.7 hours.
Can you stack Low-Dose Naltrexone with PT-141?
Stack compatibility depends on mechanism overlap, legal status, and individual response. Check each compound page for specific interactions and contraindications before combining.
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