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Isolated phytochemicals & plant compounds

D-Limonene

(R)-(+)-Limonene

D-Limonene, also called (R)-(+)-limonene, is a citrus-derived monoterpene used in food-flavor contexts and sold in some softgels. A small 2024 human vaporization study found that d-limonene modified selected anxiety-like ratings only when combined with THC; d-limonene alone did not differ from placebo. That route- and THC-specific finding does not establish oral softgel benefits for calm, focus, memory, mood, or productivity.

Isolated CompoundFood DerivedOil BasedFat SolubleClinical ResearchLimited Human EvidenceMostly Animal Evidence
Updated August 2026/6 min read/10 citations
Reviewed by the NootropicsIndex editorial team.Method: prioritize cited human research and official safety or regulatory sources; compare retailer-listed prices without endorsing products.Affiliate disclosure
01

What is it?

Human signal is route- and THC-specific6
In a small controlled study, vaporized d-limonene modified selected anxiety-like ratings when given with THC. D-limonene alone did not differ from placebo, so the result does not establish a general calm, focus, or mood effect.
A listed softgel strength is not an evidence-backed nootropic dose10
The legacy row identifies a 1000 mg softgel product. That label strength can help identify a product format, but it is not a validated cognitive, mood, or timing protocol.

What D-Limonene is

1

D-Limonene is the (R)-(+)-limonene form of a volatile citrus-derived monoterpene. The same chemical identity can occur in flavoring, fragrance, solvent, and supplement products, so a product listing should state an ingestible formulation and current label details.

No direct oral nootropic trial identified6
Reviewed sources did not identify oral D-limonene trials for focus, attention, memory, motivation, or productivity. This page therefore classifies those outcomes as evidence gaps rather than benefits.
02

Names, aliases and forms

Common NamesD-Limonene; (+)-Limonene; Citrene; Carvene
Chemical Names(R)-(+)-Limonene; (4R)-1-methyl-4-prop-1-en-2-ylcyclohexene; (+)-p-Mentha-1,8-diene
Cas Number5989-27-5
Pubchem Cid440917
Molecular FormulaC10H16
InchikeyXMGQYMWWDOXHJM-JTQLQIEISA-N
Regulatory NameFEMA No. 2633
03

Mechanisms of action

Human THC co-administration context

6

The 2024 study tested inhaled d-limonene with inhaled THC in healthy adults who intermittently use cannabis. It provides a route- and context-specific observation, not a general oral anxiolytic or nootropic mechanism.

Intestinal and stress mechanisms remain preclinical

9

Cellular intestinal-barrier findings and rat stress-model findings can guide future research questions. They do not establish human oral gastrointestinal, stress, or cognitive outcomes.

04

Potential effects and evidence map

Human evidence includes food-flavor regulatory context, limited safety and pharmacokinetic studies, and a small vaporized THC co-administration study. In that study, d-limonene alone did not differ from placebo; the selective signal concerned certain THC-related subjective ratings. No reviewed trial established oral D-limonene softgel effects for focus, memory, general calm, mood, or productivity. Animal and cell findings remain preclinical.

Effect domainMagnitudeGrade
Calm / relaxation6
AcuteConfidence: Medium

In a small vaporized THC study, d-limonene modified selected THC-related anxiety-like ratings; d-limonene alone did not differ from placebo.

Note This route- and THC-specific result does not establish oral softgel calm or relaxation effects.

1/5
C
Stress resilience7
UnknownConfidence: Low

Animal stress-model findings do not establish a human stress-resilience effect.

Note No reviewed oral human trial established stress-resilience outcomes.

0/5
D
Mood / wellbeing6
UnknownConfidence: High

No reviewed trial established an oral D-limonene effect on general mood or wellbeing.

Note The vaporized THC study did not measure baseline oral mood support.

0/5
E
Cellular / long-term brain support9
UnknownConfidence: Low

Cell and animal mechanisms are too indirect for a long-term brain-support claim.

Note Do not translate preclinical intestinal or stress mechanisms into cognitive outcomes.

0/5
D
05

Typical dosages and timing

Dose status10No nootropic dose established

The compact dosage fields are blank. A legacy 1000 mg softgel row, supervised high-dose clinical research, and vaporized THC study doses are not interchangeable consumer dosing evidence.

06

Timing & effect horizon

Effect horizonUnknown
Unknown
No oral nootropic timing field is supported5

Reviewed sources did not provide a compact oral supplement onset, duration, The time for blood levels to fall by half during the final elimination phase.Source, tolerance, or cycle field for nootropic use. The timing fields therefore remain blank.

07

Safety, side effects and risk profile

GI discomfort5
Confidence: Medium

High-dose human studies reported nausea, vomiting, and diarrhea; concentrated oral products can also be poorly tolerated by some people.

Note The source is high-dose clinical context, not a routine softgel protocol.

2/5
B
Interaction risk6
Confidence: Low

A vaporized THC study did not find a THC pharmacokinetic change, but it did find a context-specific subjective interaction. A broad oral softgel interaction map was not established.

Note Do not infer interactions with sedatives, alcohol, or other medicines from the current source set.

1/5
C
Pregnancy / lactation caution4
Confidence: Medium

Concentrated d-limonene supplement research does not establish safety for pregnancy, lactation, or childhood.

Note The food-flavor references address a separate low-exposure setting.

2/5
E
Liver / kidney caution4
Confidence: Low

Limited human data do not define liver or kidney outcomes for ordinary softgel use.

Note High-dose clinical findings and animal observations should not be converted into a routine softgel safety conclusion.

1/5
C
Headache / dizziness4
Confidence: Low

Headache and dizziness are not well quantified for oral D-limonene supplement users in the reviewed sources.

Note Do not infer frequency from aroma, topical, or high-dose clinical contexts.

1/5
E
Evidence uncertainty6
Confidence: High

The only modern human brain-adjacent signal is small, vaporized, and THC-specific; oral nootropic timing, benefit, and long-term outcome evidence is unavailable.

Note This uncertainty concerns nootropic positioning, not chemical identity or food-flavor status.

3/5
C
High-dose human context5GI effects reported

High-dose human studies reported nausea, vomiting, and diarrhea. Those data are not a routine softgel protocol, but they support keeping gastrointestinal tolerance separate from cognitive claims.

Regulatory context2Intended flavor use

U.S. food-flavor listings concern intended flavor use. They do not establish D-limonene softgel efficacy for mood, cognition, digestive outcomes, or other health outcomes.

Evidence gap4Concentrated use data limited

Reviewed sources did not establish concentrated D-limonene supplement safety during pregnancy, lactation, or childhood. Food-flavor exposure is a different context from concentrated softgel use.

08

Interactions and cautions

THC-specific context6

The vaporized study found a context-specific subjective interaction with THC and did not find a THC pharmacokinetic change. It does not establish interactions for oral D-limonene softgels with alcohol, sedatives, or other medicines.

09

Legal and regulatory status

United States, as of 2026-08-213

In the United States, limonene appears in 21 CFR 182.60 and FDA food-substance material for intended flavor use. This U.S. food-flavor context does not establish supplement efficacy or determine status in other jurisdictions.

10

How it compares

Evidence context4

Historical digestive-use discussion and food-flavor context do not establish a brain, mood, or productivity effect. Evidence categories remain separate on this profile.

Form comparison1

D-limonene softgels are not interchangeable with essential oils, solvent-grade limonene, mixed citrus oils, or multi-terpene cannabis products. Compare the stated enantiomer, ingestible formulation, carrier, and current label rather than inferring equivalence.

11

Practical buying and quality notes

  • The legacy crawl record names a Jarrow D-Limonene Softgels 1000 mg product. It has no active offer or current price information, so it cannot support a current price-per-serving comparison.10
  • The legacy record does not verify a current strength, carrier oil, lot, expiry, or test record. Use current label and seller documentation when comparing any live offer.2
  • Limonene also appears in solvent, cleaning, fragrance, and aromatherapy products. Those product categories do not establish equivalence with an ingestible softgel listing.2
12

FAQ

Is D-Limonene a proven nootropic?

6

No. The best human brain-adjacent result is a small vaporized THC co-administration study; oral focus, memory, and productivity trials were not identified.

What is the D-Limonene dose?

10

No validated oral nootropic dose was identified. A legacy 1000 mg softgel product row is a format detail, not a cognitive or calm protocol.

How long does D-Limonene last?

5

Reviewed sources did not establish oral nootropic onset, duration, half-life, or cycle fields, so the compact timing fields are blank.

Can D-Limonene reduce anxiety?

6

A 2024 study found lower selected anxiety-like ratings in one vaporized THC plus d-limonene condition. D-limonene alone did not differ from placebo, and the study did not establish an oral general-calm effect.

Is D-Limonene safe?

4

D-limonene has food-flavor context and limited human tolerability data, but concentrated softgel safety is not established for sensitive groups and high-dose studies reported GI effects.

13

References

  1. PubChem. (+)-Limonene (CID 440917): identity, stereochemistry, formula, and synonyms. Accessed 2026-08-21.
  2. FDA Substances Added to Food database. D-Limonene entry. Accessed 2026-07-01.
  3. Electronic Code of Federal Regulations. 21 CFR 182.60, Synthetic flavoring substances and adjuvants. Accessed 2026-07-01.
  4. Sun J. D-Limonene: safety and clinical applications. Altern Med Rev. 2007.
  5. Vigushin DM, et al. Phase I and pharmacokinetic study of D-limonene in patients with advanced cancer. Cancer Chemother Pharmacol. 1998.
  6. Spindle TR, et al. Vaporized D-limonene selectively modifies selected acute THC-related anxiety-like effects in healthy adults who intermittently use cannabis. Drug Alcohol Depend. 2024;257:111267. doi:10.1016/j.drugalcdep.2024.111267. PMID:38498958.
  7. Anti-stress effects of d-limonene and its metabolite perillyl alcohol. Rejuvenation Res. 2014.
  8. Effect of d-limonene and its derivatives on breast cancer in human trials: a scoping review and narrative synthesis. BMC Cancer. 2021.
  9. Dietary limonene promotes gastrointestinal barrier function via upregulating tight/adherens junction proteins through CB1R-related mechanisms. BioFactors. 2025.
  10. NootropicsIndex legacy product-listing snapshot: Jarrow d-Limonene Softgels 1000 mg via Smartpowders.
Note

This page is informational and summarizes available evidence. It is not medical advice, a recommendation, or a substitute for guidance from a qualified clinician.