Peptide Profile
Substance P Antagonists
NK1 receptor blockers that reduce pain signals and nausea at the source
Dose Range
80 mg-125 mgmg
Frequency
Once daily
Route
Oral capsule
Cycle Length
Ongoing/indefinite
Onset
Moderate (1-2 weeks)
Evidence
Moderate
Compound Profile
Scientific & Efficacy Data
C23H21F7N4O3
Molecular Formula
534.4 g/mol
Molecular Weight
9-13 hours (elimination half-life)
Half-Life
Approximately 60-65% oral bioavailability; food may increase absorption
Bioavailability
170729-80-3
CAS #
135413536
PubChem ID ↗
Developed By · 1990
Research Team
Multiple Pharmaceutical Companies
Primary Benefits
Exceptional effectiveness at blocking chemotherapy-induced nausea and vomiting through NK1 receptor blockade
Reduces pain transmission by blocking substance P, a key neurotransmitter in pain pathways
Protects nerve cells from inflammatory damage and reduces neurogenic inflammation
Amino Acid Sequence
Not a peptide sequence; aprepitant is a small-molecule non-peptide antagonist that blocks substance P bindingDosing
How much
do I take?
Timing
Best time to take
Take Substance P Antagonists at the same time each day for consistent blood levels. Morning dosing with breakfast is often preferred, but follow your healthcare provider's specific instructions.
With food?
Substance P Antagonists can typically be taken with or without food. Taking it with a light meal may help reduce any GI discomfort. Avoid taking with grapefruit juice or high-fat meals unless specifically directed.
If stacking
Substance P Antagonists should be used as directed by your healthcare provider. If combining with other medications or supplements, discuss potential interactions with your provider. Avoid combining with compounds that have overlapping mechanisms unless specifically guided by a medical professional.
Adjusting Your Dose
Increase if
- +You've tolerated the current dose for the recommended period without significant side effects
- +Therapeutic goals haven't been met at the current dose level
- +Your healthcare provider recommends dose escalation based on your response
- +Lab work or clinical assessments support a higher dose
Decrease if
- -Side effects are bothersome or impacting daily life despite management strategies
- -You experience any signs of an adverse reaction
- -Lab results indicate the need for dose reduction
- -Your healthcare provider recommends a lower dose based on your response
Signs of right dose
- ✓Therapeutic goals being met with minimal side effects
- ✓Stable and consistent response to treatment
- ✓Lab values or clinical markers trending in the right direction
- ✓Good tolerance with manageable or absent side effects
Dosing Calculator
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Suitability
Is this
right for me?
Best For
Managing severe nausea from cancer treatments
Substance P Antagonists is particularly well-suited for individuals focused on managing severe nausea from cancer treatments. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Chronic pain reduction
Substance P Antagonists is particularly well-suited for individuals focused on chronic pain reduction. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Improving quality of life during intensive medical therapy
Substance P Antagonists is particularly well-suited for individuals focused on improving quality of life during intensive medical therapy. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Consider Alternatives If
Who Should Avoid
Do not use if
- ×Severe hypersensitivity to aprepitant or any component
- ×Concurrent use with certain other medications that affect the liver
- ×Severe cardiac conditions
Use with caution if
- !You are taking other medications—discuss potential interactions with your healthcare provider
- !You have a history of liver or kidney disease
- !You are elderly or have multiple medical conditions
- !You are planning surgery in the near future—inform your surgeon about Substance P Antagonists use
- !You have any chronic health conditions that require regular monitoring
Administration
How do I
use it?
Reconstitution
What you need
- •Substance P Antagonists in its prescribed form
- •Clean, dry storage container
- •Measuring device if applicable (oral syringe, measuring cup)
- •Calendar or reminder app for dosing schedule
Injection
Route
Substance P Antagonists is administered Oral capsule—no injection required
Best sites
- •Not applicable—this is not an injectable formulation
Technique
- 1.Follow the specific administration instructions for your Substance P Antagonists formulation
- 2.Take or apply as directed by your healthcare provider
- 3.Store properly between uses according to package instructions
Storage
Signs of degradation
Sample Daily Schedule
Safety
Is it
safe?
Safety Profile
Aprepitant (the primary NK1 antagonist) has been FDA-approved since 2003 with extensive safety data in over 50,000 cancer patients receiving highly emetogenic chemotherapy. Most common adverse events are mild to moderate—headache (15-20%), fatigue, and constipation—which are often difficult to attribute solely to aprepitant versus underlying malignancy or chemotherapy effects. Serious but rare adverse events include Stevens-Johnson syndrome (extremely uncommon) and QT prolongation (in susceptible individuals), requiring baseline ECG evaluation in high-risk patients.
Safety evidence derives from Phase 3 chemotherapy-induced nausea trials, pediatric studies with weight-based dosing, and 20+ years of post-market pharmacovigilance. Off-label pain and psychiatric applications have accumulating clinical experience but lack the robust safety database of CINV indication. Important CYP3A4 drug interaction potential requires careful medication reconciliation before each dose.
Common Side Effects
Experienced by some users
Headache
One of the most common side effects, occurring in 15-20% of patients. Usually develops within the first few hours of dosing and typically resolves within 24 hours.
Management: Take over-the-counter pain relievers like acetaminophen or ibuprofen. Stay hydrated. If persistent, inform your doctor.
Fatigue or weakness
Some patients report feeling tired or having low energy, particularly on the second or third day of the 3-day regimen. This usually improves after treatment ends.
Management: Get adequate rest. Avoid driving or operating machinery if severely fatigued. This side effect typically resolves within 1-2 days.
Constipation
Occurs in about 10% of patients. Substance P antagonists can slow intestinal movement. More common when combined with opioid pain medications or other antiemetics.
Management: Increase fiber intake through fruits, vegetables, and whole grains. Drink 8-10 glasses of water daily. Ask your doctor about stool softeners or gentle laxatives if needed.
Less Common
- •Loss of appetite
- •Dizziness
These typically resolve with continued use or dose adjustment.
Stop and Seek Help If
- ×Severe or worsening side effects that don't improve with dose adjustment or supportive care
- ×Signs of an allergic reaction—rash, hives, swelling, or difficulty breathing
- ×Your healthcare provider recommends discontinuation based on your clinical response
- ×Development of any new medical condition that may be contraindicated with Substance P Antagonists
- ×Pregnancy or planning to become pregnant (unless specifically approved for use during pregnancy)
- ×Abnormal lab results or clinical markers that suggest adverse effects
Substance P Antagonists should only be started, adjusted, or discontinued under medical supervision. This information is for educational purposes only and does not replace professional medical advice. Never stop a prescribed treatment without consulting your healthcare provider first, as abrupt discontinuation may have consequences.
Interactions
With other peptides
- ✓Enhance anti-nausea effects through different mechanisms of action
- ✓Provide additional anti-inflammatory and antiemetic benefits
- ✓Broader neurokinin receptor coverage for enhanced pain relief
With medications
- !Strong CYP3A4 inhibitors (like ketoconazole, ritonavir) - risk of increased aprepitant levels - Use with caution—discuss with your healthcare provider.
- !Pimozide - risk of serious arrhythmias - Use with caution—discuss with your healthcare provider.
With supplements
- ✓Multivitamins - Generally safe to take alongside Substance P Antagonists. Space doses apart if taking oral formulations to ensure optimal absorption.
- ✓Electrolyte supplements - Helpful if experiencing any GI side effects that could lead to dehydration. Safe to combine.
Effectiveness
Does it
work?
Evidence Level
Moderate human trials
What to Expect
Immediate (0-1 hour) (First hour after taking aprepitant)
What you might notice
- •Drug is absorbed and begins reaching peak plasma concentration
- •You may notice early side effects like mild headache starting to develop
- •If taken before chemotherapy, it's beginning to block NK1 receptors in anticipation of nausea signals
What's normal
- •Initial response to Substance P Antagonists is beginning at the cellular level
- •Different individuals experience Substance P Antagonists's onset at different rates
- •Transient systemic effects from initial Substance P Antagonists exposure are common
What's next
- →Maintain consistent Substance P Antagonists administration as prescribed
- →Document subjective effects and physical markers daily
- →Schedule a check-in with your provider about initial observations
Early Response (2-6 hours) (Hours 2-6 after dosing)
What you might notice
- •Peak plasma concentration reached
- •Maximum NK1 receptor blockade is occurring throughout the central nervous system
- •Most patients notice significant reduction in nausea if chemotherapy is ongoing
- •Headaches, if occurring, are usually at their peak now
What's normal
- •Substance P Antagonists is achieving sufficient receptor engagement
- •Initial mechanism of Substance P Antagonists is taking effect
- •Early transient effects from Substance P Antagonists administration are resolving
What's next
- →Maintain consistent Substance P Antagonists administration as prescribed
- →Document subjective effects and physical markers daily
- →Schedule a check-in with your provider about initial observations
Sustained Effect (24-72 hours) (Throughout the 3-day treatment period)
What you might notice
- •The drug's long 9-13 hour half-life means it accumulates in your system, providing sustained NK1 receptor blockade
- •By Day 2 and Day 3, blood levels are higher and more stable
- •This creates a protective umbrella against delayed nausea and vomiting that can occur 24-72 hours after chemotherapy
What's normal
- •Substance P Antagonists response patterns are emerging
- •Initial Substance P Antagonists response is consistent with mechanism expectations
- •Early tolerance development to Substance P Antagonists is not expected
What's next
- →Assess whether Substance P Antagonists response aligns with expectations
- →Plan next steps based on initial Substance P Antagonists tolerance and response
- →Establish baseline monitoring for Substance P Antagonists response tracking
Signs It's Working
Treatment Response
- ✓Improvement in the primary symptoms or condition being treated
- ✓Positive changes in relevant lab values or clinical markers
- ✓Consistent, stable response to Substance P Antagonists over time
- ✓Reduction in symptom frequency or severity
General Well-being
- ✓Improved energy levels and daily functioning
- ✓Better quality of life related to the treated condition
- ✓Manageable or absent side effects indicating good tolerance
- ✓Positive feedback from healthcare provider during check-ups
Not Seeing Results?
Common reasons
- •Not at therapeutic dose yet—initial doses are for building tolerance, not maximum effect
- •Insufficient time at target dose—most compounds need several weeks to show full benefits
- •Inconsistent dosing schedule—regular, consistent use is crucial for optimal results
- •Individual variation in response—genetics, metabolism, and other factors affect outcomes
- •Underlying conditions or medications interfering with absorption or effectiveness
- •Improper storage leading to degraded product—always verify proper storage conditions
Key Research
"Involvement of ASIC3 and Substance P in Therapeutic Ultrasound-Mediated Analgesia in Mouse Models of Fibromyalgia"
Research investigators, 2023
Finding: Substance P and ASIC3 channels mediated pain in fibromyalgia models, with antagonists abolishing pain responses. NK1 receptor blockade reduced mechanical hyperalgesia through ASIC3-containing channels in muscle afferents.
View Study"Involvement of the substance P/neurokinin-1 receptor system in oral pain and inflammation"
Research investigators, 2020
Finding: Substance P antagonists effectively reduced oral pain and inflammation through NK1 receptor blockade. The system plays a critical role in chemotherapy-induced mucositis and inflammatory pain conditions.
View Study"Advances in the research and application of neurokinin-1 receptor antagonists"
Research investigators, 2024
Finding: NK1 antagonists demonstrated therapeutic potential across multiple indications including nausea, pain, depression, and anxiety. Beyond chemotherapy-induced nausea, these antagonists show promise for psychiatric and neurological conditions.
View Study"Trigeminal nerve-driven neurogenic inflammation linking migraine to glioblastoma invasion: a literature review"
Research investigators, 2025
Finding: Substance P released from trigeminal nerves drives neurogenic inflammation through CGRP, SP, and PACAP pathways. Antagonists like aprepitant show therapeutic potential for migraine management through blocking these inflammatory mediators.
View StudyFrequently Asked Questions