This SQL script builds the CDM v5 DRUG_ERA table from drug exposures. It rolls up the drug exposures to the ingredient form, and then creates the eras for each ingredient concept id.

Drug Era Builder v5

with cteDrugTarget (DRUG_EXPOSURE_ID, PERSON_ID, DRUG_CONCEPT_ID, DRUG_TYPE_CONCEPT_ID, DRUG_EXPOSURE_START_DATE, DRUG_EXPOSURE_END_DATE) as
(
-- Normalize DRUG_EXPOSURE_END_DATE to either the existing drug exposure end date, or add days supply, or add 1 day to the start date
	select d.DRUG_EXPOSURE_ID, d. PERSON_ID, c.CONCEPT_ID, d.DRUG_TYPE_CONCEPT_ID, DRUG_EXPOSURE_START_DATE, 
		COALESCE(DRUG_EXPOSURE_END_DATE, DATEADD(day,DAYS_SUPPLY,DRUG_EXPOSURE_START_DATE), DATEADD(day,1,DRUG_EXPOSURE_START_DATE)) as DRUG_EXPOSURE_END_DATE
	FROM DRUG_EXPOSURE d
		join CONCEPT_ANCESTOR ca on ca.DESCENDANT_CONCEPT_ID = d.DRUG_CONCEPT_ID
		join CONCEPT c on ca.ANCESTOR_CONCEPT_ID = c.CONCEPT_ID
		where c.VOCABULARY_ID = 'RxNorm'
		and c.CONCEPT_CLASS_ID = 'Ingredient'
),
cteEndDates (PERSON_ID, DRUG_CONCEPT_ID, END_DATE) as -- the magic
(
	select PERSON_ID, DRUG_CONCEPT_ID, DATEADD(day,-30,EVENT_DATE) as END_DATE -- unpad the end date
	FROM
	(
		select PERSON_ID, DRUG_CONCEPT_ID, EVENT_DATE, EVENT_TYPE, 
		MAX(START_ORDINAL) OVER (PARTITION BY PERSON_ID, DRUG_CONCEPT_ID ORDER BY EVENT_DATE, EVENT_TYPE ROWS UNBOUNDED PRECEDING) as START_ORDINAL, -- this pulls the current START down from the prior rows so that the NULLs from the END DATES will contain a value we can compare with 
		ROW_NUMBER() OVER (PARTITION BY PERSON_ID, DRUG_CONCEPT_ID ORDER BY EVENT_DATE, EVENT_TYPE) AS OVERALL_ORD -- this re-numbers the inner UNION so all rows are numbered ordered by the event date
		from
		(
			-- select the start dates, assigning a row number to each
			Select PERSON_ID, DRUG_CONCEPT_ID, DRUG_EXPOSURE_START_DATE AS EVENT_DATE, -1 as EVENT_TYPE, ROW_NUMBER() OVER (PARTITION BY PERSON_ID, DRUG_CONCEPT_ID ORDER BY DRUG_EXPOSURE_START_DATE) as START_ORDINAL
			from cteDrugTarget
		
			UNION ALL
		
			-- pad the end dates by 30 to allow a grace period for overlapping ranges.
			select PERSON_ID, DRUG_CONCEPT_ID, DATEADD(day,30,DRUG_EXPOSURE_END_DATE), 1 as EVENT_TYPE, NULL
			FROM cteDrugTarget
		) RAWDATA
	) E
	WHERE (2 * E.START_ORDINAL) - E.OVERALL_ORD = 0
),
cteDrugExposureEnds (PERSON_ID, DRUG_CONCEPT_ID, DRUG_TYPE_CONCEPT_ID, DRUG_EXPOSURE_START_DATE, DRUG_ERA_END_DATE) as
(
select 
	d.PERSON_ID, 
	d.DRUG_CONCEPT_ID,
	d.DRUG_TYPE_CONCEPT_ID,
	d.DRUG_EXPOSURE_START_DATE, 
	MIN(e.END_DATE) as ERA_END_DATE
FROM cteDrugTarget d
JOIN cteEndDates e on d.PERSON_ID = e.PERSON_ID and d.DRUG_CONCEPT_ID = e.DRUG_CONCEPT_ID and e.END_DATE >= d.DRUG_EXPOSURE_START_DATE
GROUP BY d.DRUG_EXPOSURE_ID, 
	d.PERSON_ID, 
	d.DRUG_CONCEPT_ID, 
	d.DRUG_TYPE_CONCEPT_ID, 
	d.DRUG_EXPOSURE_START_DATE
)
-- Add INSERT statement here
select person_id, drug_concept_id, drug_type_concept_id, min(DRUG_EXPOSURE_START_DATE) as DRUG_ERA_START_DATE, DRUG_ERA_END_DATE, COUNT(*) as DRUG_EXPOSURE_COUNT
from cteDrugExposureEnds
GROUP BY person_id, drug_concept_id, drug_type_concept_id, DRUG_ERA_END_DATE
order by person_id, drug_concept_id
;

Trying to understand the code (I'm a bit slow). Could you explain why in line 24 you partition by drug_concept_id, not ingredient_concept_id?

Good eye, but there's something confusing about the drugTarget CTE: This select:

select d.DRUG_EXPOSURE_ID, d. PERSON_ID, c.CONCEPT_ID, d.DRUG_TYPE_CONCEPT_ID, DRUG_EXPOSURE_START_DATE, 
        COALESCE(DRUG_EXPOSURE_END_DATE, DATEADD(day,DAYS_SUPPLY,DRUG_EXPOSURE_START_DATE), DATEADD(day,1,DRUG_EXPOSURE_START_DATE)) as DRUG_EXPOSURE_END_DATE,
        c.CONCEPT_ID as INGREDIENT_CONCEPT_ID

notice how i'm selecting c.Concept_ID as both the DRUG_CONCEPT_ID as well as the INGREDIENT_CONCEPT_ID. I think when adding the 'rollup to ingredient' logic, I got lazy by changing the meaning of DRUG_CONCEPT_ID to be the ingredient and then decided later to add an actual INGREDIENT_CONCEPT_ID. I'll clean up the above query to eliminate the INGREDIENT_CONCEPT_ID.