2026 ICD-10-CM Diagnosis Code T40.995AAdverse effect of other psychodysleptics [hallucinogens], initial encounter
T40.995A is a billable ICD-10-CM diagnosis code for adverse effect of other psychodysleptics [hallucinogens], initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as adverse reaction to hallucinogen. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter; and Hallucinogen-related disorders.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T40.995A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adverse reaction to hallucinogen
- Adverse reaction to mescaline
- Adverse reaction to psilocin
- Adverse reaction to psilocybin
Coding GuidelinesGuidance
When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of narcotics and psychodysleptics [hallucinogens] (T40). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Phencyclidine
a hallucinogen formerly used as a veterinary anesthetic, and briefly as a general anesthetic for humans. phencyclidine is similar to ketamine in structure and in many of its effects. like ketamine, it can produce a dissociative state. it exerts its pharmacological action through inhibition of nmda receptors (receptors, n-methyl-d-aspartate). as a drug of abuse, it is known as pcp and angel dust.Phencyclidine Abuse
the misuse of phencyclidine with associated psychological symptoms and impairment in social or occupational functioning.Receptors, Phencyclidine
specific sites or molecular structures on cell membranes or in cells with which phencyclidine reacts or to which it binds to elicit the specific response of the cell to phencyclidine. studies have demonstrated the presence of multiple receptor sites for pcp. these are the pcp/sigma site, which binds both pcp and psychotomimetic opiates but not certain antipsychotics, and the pcp site, which selectively binds pcp analogs.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T40.995A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T40.995AOverview
Is T40.995A (Adverse effect of other psychodysleptics [hallucinogens]) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of other psychodysleptics [hallucinogens], initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T40.995A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of other psychodysleptics [hallucinogens], such as an emergency visit or first evaluation.
What MS-DRG does T40.995A group to?
On inpatient claims, adverse effect of other psychodysleptics [hallucinogens], initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T40.995A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of other psychodysleptics [hallucinogens], initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
What is the ICD-9 equivalent of T40.995A?
Under the General Equivalence Mappings, adverse effect of other psychodysleptics [hallucinogens], initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E939.6 (adv eff hallucinogens). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
