A Randomized Controlled Test of the Effects of CHI-554 on Fear.

1. Person is between 18 and 55-years-old (inclusive).
2. Person has a BMI between 18 and 35 kg/m2 (inclusive).
3. Person is willing and able to provide informed consent and attend a 3.5-hour, in-person session.
4. Woman of childbearing potential must not be pregnant or currently breastfeeding.
5. If person uses medication, the person has maintained a stable dose and regimen on existing medications for at least 30 days prior to participation in the study and throughout the study.
6. Person agrees to abide by all study restrictions and comply with all study procedures.

Exclusion Criteria:

1. Person has a known history of significant allergic condition, significant hypersensitivity to the IP, or allergic reaction to cannabis, cannabinoid medications, hemp products, or excipients of the IP.
2. Person has been exposed to any investigational drug or device \< 30 days prior to screening or plans to take an investigational drug in the near future (within 30 days).
3. Person has used cannabis, synthetic cannabinoid or cannabinoid analogue (e.g., dronabinol, nabilone), synthetic cannabinoid receptor agonist (e.g., spice, K2), or any CBD- or delta-9- tetrahydrocannabinol (THC)-containing product within 30 days of screening or during the study.
4. Person is currently prescribed medications with likely THC- or CBD- interactions (e.g., warfarin, clobazam, valproic acid, phenobarbital, mechanistic target of rapamycin [mTOR] inhibitors, oral tacrolimus, St. John's wort; Epidiolex).
5. Person is currently prescribed and using a medication used in the treatment of anxiety disorders (e.g., selective serotonin uptake inhibitors, venlafaxine, buspirone, benzodiazepines, hydroxyzine, tiagabine, gabapentin, valproate, lamotrigine, topiramate, beta blockers, clonidine, guanfacine, atypical antipsychotics);
6. Person has a positive drug screen for THC, barbiturates, amphetamines, benzodiazepines, and/or opiates at baseline assessment.
7. Person meets diagnostic criteria for a current DSM-5 diagnosis indexed via the MINI.
8. Person meets criteria for a lifetime history of an unexpected or unprovoked panic attack indexed via the MINI.
9. Person endorses current suicidal intent as indexed via the C-SSRS.
10. Person reports a history of being diagnosed with a respiratory or lung disease (including asthma attacks), cardiac or pulmonary disease, epilepsy, narcolepsy, sleep apnea, anemia, or renal disease during a medical history interview.
11. Person has participated in a study that used a CO2-enriched air procedure.
12. Person has received formal training to tolerate elevated levels of CO2 or bodily arousal (such as free diver training or interoceptive exposure-based treatment).
13. Any other clinically significant disease or disorder or abnormal findings during screening or the baseline assessment that, in the opinion of the investigator, may either put the person at risk because of participation in the study, may confound the results of the study, or affect the person's ability to participate in the study.
14. Person has an acute or progressive disease that is likely to interfere with the objectives of the study, or the ability to adhere to protocol requirements.
15. Woman of childbearing potential, unless she has not engaged in vaginal intercourse or she has used effective contraception when doing so (for example, oral contraception, double barrier, intra-uterine device) for at least 30 days prior to the study.
16. Woman of childbearing potential, unless willing to ensure that she or her partner use effective contraception (for example, oral contraception, double barrier, intra-uterine device) during the study and for 30 days thereafter (however, a male condom should not be used in conjunction with a female condom).
17. Man whose partner is of childbearing potential, unless willing to ensure that he or his partner use effective contraception (for example, oral contraception, double barrier, intra-uterine device) during the study and for 30 days thereafter (however, a male condom should not be used in conjunction with a female condom).
18. Person has history of diagnosis related to hepatic function and/or significantly impaired hepatic function (alanine aminotransferase [ALT] >5 ´ upper limit of normal [ULN] or total bilirubin [TBL] >2 ´ ULN) OR the ALT or aspartate aminotransferase (AST) >3 ´ ULN and TBL >2 ´ ULN (or international normalized ratio [INR] >1.5).
19. Person demonstrates behavior indicating unreliability or inability to comply with the requirements of the protocol.