ICD code T40.901S – Unspecified psychodysleptic poisoning, accidental, sequela

Key takeaways

T40.901S reports the residual effects of an accidental hallucinogen poisoning, not the poisoning event itself.

The 7th character S applies only once the poisoning episode has resolved and treatment for it has ended.

Sequence the residual condition first, then T40.901S as an additional diagnosis.

External cause codes from X40 to X44 are recommended companions, though payer requirements vary.

Hallucinogen use disorder belongs to the F16 series, and coding it here is a routine denial trigger.

What ICD-10 code T40.901S covers, and why it is billable

ICD-10 code T40.901S is the billable diagnosis code for poisoning by unspecified psychodysleptics [hallucinogens], accidental (unintentional), sequela. It reports a residual condition left behind by an accidental hallucinogen poisoning that has already run its course.

The code is valid for the 2026 edition, effective October 1, 2025. The CDC/NCHS ICD-10-CM web tool lists it as a specific, billable code. Nothing more granular is needed before you put it on a claim.

Three attributes are packed into that descriptor. Substance class is unspecified psychodysleptics, intent is accidental, and encounter type is sequela. Each one has to be supported somewhere in the chart, and the third is where most of these claims come apart.

Every character in T40.901S carries a coding decision

Each position in the code encodes one decision, and misreading a single position is the fastest route to a denial. The table below decodes them in order.

Character 6 already carries the intent, so no separate intent qualifier is needed. What the chart still has to do is rule out self-harm and assault, because the accidental designation rests on that.

The 7th character decides the encounter: A, D, or S

The 7th character tells the payer which phase of care the visit belongs to. Choose the wrong one and the claim contradicts the note, which is a routine rejection trigger on T40.9 codes.

A sequela is a condition that persists after the poisoning episode has closed. The poisoning is no longer the reason for the visit. The residual condition is, and Chapter 19 sequences the sequela code after that condition rather than before it.

Which residual conditions qualify as a sequela?

Residual conditions after accidental hallucinogen poisoning include hallucinogen persisting perception disorder (HPPD) and persistent psychosis.

Cognitive dysfunction and mood or anxiety disturbance also qualify when they trace back to the poisoning. The treating provider has to document the condition. A coder cannot infer it from the visit narrative alone.

When the record leaves room for doubt, work the three questions below in order and stop at the first yes.

Psychodysleptics are hallucinogens, not narcotics

Psychodysleptics are substances that alter perception, mood, and cognition. ICD-10-CM treats “psychodysleptic” and “hallucinogen” as the same thing inside T40, which is why the descriptor carries both words.

The unspecified designation in T40.901S applies when the agent is not documented or cannot be determined. Where the substance is named, a more specific code usually exists, so check before you default to the unspecified option.

• Classic hallucinogens: LSD has its own subcategory at T40.8X, while psilocybin, mescaline, and dimethyltryptamine (DMT) code to T40.99x as other psychodysleptics
• Dissociative hallucinogens: phencyclidine (PCP) codes to T40.99x, and ketamine sits outside T40 altogether at T41.29x with the general anesthetics
• Unspecified: T40.901S applies when the record names a hallucinogen but not which one
• Outside this branch: opioid poisoning (T40.0-T40.6), cannabis (T40.7), and stimulants (T43.6x)

T40.9 is not an opioid code. Grouping T40.9x codes with the opioid poisoning codes at T40.0 through T40.6 is a substantive error. The two branches stay separate in every annual update file.

T40.901S sits five levels down the T40 hierarchy

Reading the tree from the top shows why unspecified is a last resort. Each level narrows the substance, then the intent, then the encounter, and only the bottom row is billable.

Poisoning, adverse effect, or underdosing: the prescription decides

One question separates the three. Was the substance taken as a valid prescription directs? If it was, an adverse effect or underdosing code applies. If it was not, the encounter is a poisoning.

Intent in the chart drives the choice. Where the record says nothing about intent, the ICD-10-CM guidelines default to accidental rather than undetermined. Undetermined intent is held back for notes that state the intent could not be established.

The codes that sit closest to T40.901S

Six codes come up again and again beside this one. Keeping them in one reference cuts the cross-code confusion that slows a denial review down.

T40.901S is rarely coded alone, and never coded first

Chapter 19 puts the residual condition in the first-listed position and T40.901S after it. The sequela code is there to explain where the residual condition came from, so it supports the primary diagnosis rather than replacing it.

• Residual condition code, first: the condition actually being treated, such as F16.983 for hallucinogen persisting perception disorder, a psychosis code, or a cognitive impairment code
• T40.901S, additional: names the prior accidental hallucinogen poisoning as the source of that residual condition
• External cause codes, X40-X44: report the accidental poisoning event itself, and payer requirements vary, with some payers waiving them on outpatient claims
• Activity codes, Y93.x: optional in most settings, though some payers ask for them on inpatient claims

When one of these claims comes back denied, the cause is usually one of two things. Either the sequencing is inverted, or a companion code the payer wanted is missing. Both surface on the remittance rather than at submission, so a standing denial management review finds them faster than re-reading the claim form.

What has to be in the chart before you submit T40.901S

Three documentation elements hold this code up at audit. Practices that lose T40.901S claims on retrospective review are almost always missing one of them.

• A prior poisoning event on record: the chart or transfer documentation has to reference an earlier episode of accidental hallucinogen poisoning. Verbal history alone will not carry it, so the event should appear in a previous encounter note, an ED record, or a documented intake history.
• A causal link between that event and the current condition: the treating provider states that the residual condition follows from the poisoning. Persistent perceptual disturbance and cognitive change are the usual examples. An independent psychiatric condition or ongoing substance use does not qualify.
• Confirmation the poisoning has resolved: sequela coding starts once the active poisoning is over. If the patient is still being treated for the poisoning itself, T40.901D is the correct code.

Practices that template these three checkpoints into the encounter note stop querying the provider after the fact. A structured intake that prompts for prior substance history, causal attribution, and current episode status gives the coder what they need the first time.

A 60-second check before the claim goes out

• The note names a residual condition, not the poisoning episode, as the reason for the visit.
• A prior accidental hallucinogen poisoning appears somewhere in the record.
• The provider says, in their own words, that one caused the other.
• The residual condition code sits in the first diagnosis position, with T40.901S after it.
• Intent reads as accidental, with self-harm and assault ruled out.
• Any external cause code your payer requires is attached.

Two mistakes that cause most of the rework

The first is reporting T40.901S while the poisoning is still being treated, which is T40.901D territory. The second is reaching for it on a hallucinogen use disorder visit, where the F16 series applies instead. Both are cheap to catch at coding and expensive to unpick after payment.

What Chapter 19 says about sequencing a poisoning sequela

Chapter 19 governs every T40.9x code, and its sequencing rules produce most of the errors on sequela encounters. The CMS ICD-10-CM coding guidelines set out the following.

• The residual condition is sequenced first, and T40.901S follows it as an additional diagnosis
• The 7th character S applies only after the poisoning episode has resolved, so ongoing treatment for the poisoning takes D instead
• External cause codes from the X40-X44 range are assigned as additional codes, never sequenced ahead of T40.901S
• Accidental intent needs no separate intent-of-injury code, because character 6 already carries it
• Both the poisoning code and the condition it caused are reported, so the claim shows the full clinical picture

Behavioral health and addiction medicine practices meet T40.9x codes often enough that these rules belong in the written coding policy. Leaving them to memory is how the sequencing flips on a busy afternoon.

Your T40.9 coding feeds CDC drug surveillance data

T40.9x codes do two jobs at once. They pay the claim, and they feed the national drug use datasets held by the CDC National Center for Health Statistics. A submitted T40.901S claim lands in hospital discharge data, emergency department databases, and vital statistics registries.

That gives miscoding a second cost. Using T40.901A on what is really a sequela visit inflates the count of active hallucinogen poisonings and shrinks the count of residual ones. Research indexed at NCBI has used T40.9 codes to classify psychodysleptic use in Medicare data. Claim-level accuracy reaches research-grade datasets more directly than most coders expect.

Terms that point to T40.901S in a coding search

Coders searching by term rather than by number meet these variants in EHR and encoder software. All of them resolve to T40.901S.

• Sequela of accidental poisoning by hallucinogen
• Late effect of unintentional psychodysleptic poisoning
• Residual condition following accidental psychedelic poisoning
• Sequela of accidental poisoning by unspecified psychodysleptics
• Hallucinogen poisoning sequela, accidental

None of them name a substance. Where the record does name one, check the more specific options in the ICD-10-CM code index before you fall back to the unspecified designation.

How Pabau keeps sequela claims moving from code to payment

Most of the work above happens in two places that rarely talk to each other. The clinical note lives in the chart, and the diagnosis codes get keyed into a claim somewhere else. Every rekeying step is another chance for the sequencing to flip.

Pabau, a practice management software platform for medical and aesthetic practices, keeps both on one record. Codes are looked up and pulled from the encounter itself, and required fields are checked before the claim is released. Claims go out through the clearinghouse from the same screen, and remittances come back against the same invoice.

The encounter-type call still belongs to the coder and the note. Pabau’s claims management software handles the mechanical part around it. That means less retyping, fewer missing companion codes, and a remittance that lands against the right invoice.

Track claims from code to payment

Pabau connects ICD-10 code lookup, claim submission, and remittance tracking on one patient record. See how it works for behavioral health and addiction medicine practices.

Book a demo

Conclusion

Assigning T40.901S takes seconds. Defending it takes documentation, because the chart carries every element that makes the code correct. A prior accidental poisoning, a current residual condition, and a provider statement joining the two.

Get the sequencing right and most of the trouble disappears. The residual condition leads, T40.901S follows, and the encounter type matches the phase of care the note describes. Practices that write those checks into the coding policy stop rediscovering them one denial at a time.

Book a demo to see how Pabau keeps the coded diagnosis, the claim, and the remittance on a single patient record.

Continue your research

Need a denial tracking workflow for T40.9x claims? Denial management in healthcare covers how to build a systematic denial review and appeal process for substance-related codes.

Want to understand how electronic claims move from submission to payment? Electronic claims clearinghouse explains how clearinghouse routing and remittance matching work for behavioral health practices.

Looking for revenue cycle guidance for addiction medicine billing? Revenue cycle management fundamentals covers the end-to-end process from code selection through payment posting.

Frequently asked questions