68.1%
of a 395-person subgroup reported a forgetfulness-related reason
Adults 18+ · Evidence-graded review
When executive dysfunction looks like a choice
In adult ADHD, a deliberate skip can begin with forgetting, friction, side effects, or scarcity. The final decision may be conscious even when symptoms or constraints shaped the path to it.
Strong
Moderate
Weak
Contested
Anecdotal
47
qualitative studies of adult stimulant-use motivations
90
adults in a prospective-memory study: 45 with ADHD, 45 controls
12.17M
adults in a seven-country medication-adherence cohort
0
validated adult tests that can tell why a dose was missed
We know it happens. We do not know how often
Studies document forgetting, deliberate tailoring, side-effect tradeoffs, and rationing. They do not show how often a stated choice began as an executive failure—or whether the pattern is more common in predominantly inattentive ADHD (ADHD-PI).
Start with the event
A missed dose has a before, a moment, and an after
Most studies see only the end result. This framework separates the plan, access, intention, execution, and later explanation. It is a research model, not a clinical test.
Walk through one dose
Change the four details below. The result shows why a single event may resist a clean intentional-versus-accidental label. It does not assess a person or medication regimen.
What adult studies show
The reasons overlap—often in the same person
In a U.S. survey of 602 adults treated with stimulants, 395 were classified as low or medium adherers after endorsing at least one reason. The categories overlapped heavily.
Reasons reported by low- and medium-adherence adults
Share of the 395-person subgroup endorsing each domain. One person could count in several.
Overlapping total: 212.6%
These percentages overlap. Adding them does not produce a prevalence estimate. The study also could not identify one primary cause for each person. [2]
The pattern is not limited to ADHD medication
Two studies looked at behavior rather than relying only on explanations recalled later.
Seven-country cohort · 12,174,321 adults starting blood-pressure medication
ADHD vs no ADHD · 1 year
1.45
OR for PDC-defined poor adherence95% CI 1.26–1.67
ADHD vs no ADHD · 5 years
1.64
OR for poor adherence95% CI 1.34–2.00
Within ADHD, medicated · 1 year
0.66
OR for poor adherence95% CI 0.60–0.73
Within ADHD, medicated · 5 years
0.58
OR for poor adherence95% CI 0.46–0.72
The pattern is consistent with a broader difficulty carrying out medication plans. It does not prove why: PDC measures possession, ADHD treatment may track healthcare engagement, and confounding remains. [34]
How underuse may make the next dose harder
Each link has some support. No adult study has tested the whole loop from start to finish.
1 · Existing burden
Following the plan is itself an executive task
Partial response, uncovered time, poor sleep, or comorbidity can raise the effort needed to plan and act.
2 · A plan slips
A dose, refill, or appointment is missed
The breakdown may be accidental, deliberate, or both.
3 · Exposure falls
Symptoms and daily friction return
Organization, time management, and emotional regulation may worsen.
4 · The person adapts
Medication is saved for selected days
Work gets priority; evenings, weekends, and home tasks may become routinely uncovered.
5 · A shorthand forms
The pattern becomes a personal rule
“I take it only when I need it” may be true, incomplete, or both.
Why adults take less
The reasons are practical, personal, and often mixed
A conscious decision can be constrained. An executive failure can still involve agency. These categories often overlap.
What research can see
The data can show a gap. It cannot explain it
Open each method to see what it captures—and what stays invisible.
No test can read motive
Fills, pill counts, electronic caps, drug levels, rating scales, CPTs, QbTest, pulse, and blood pressure cannot tell why one adult took less than prescribed. A stronger study would combine real-time intent, access, timing, immediate reason capture, later recall, and function.
Other explanations
Residual symptoms do not tell you why treatment fell short
The same experience can come from incomplete effect, short coverage, inconsistent use, poor sleep, another condition, substances, pharmacokinetics, or changing demands.
Predominantly inattentive presentation
For inattentive ADHD, the question matters—and the evidence is thin
Planning, activation, prospective memory, working memory, time management, and cognitive disengagement all fit the lived concerns of ADHD-PI. Most studies do not test whether the path to medication underuse differs by presentation.
What the evidence supports
- Executive and prospective-memory problems can interfere with taking medication as planned.
- Executive-function and functional scales can reveal burdens that core symptom scales miss.
- Cognitive disengagement can mimic residual inattention or “brain fog.”
- When self-awareness differs, the gap appears domain-specific rather than global.
What the evidence does not show
- Adults with ADHD-PI deliberately take less medication more often.
- A PI-specific symptom cluster proves inadequate exposure.
- Inattention requires systematically different exposure than hyperactivity in adults.
- Executive dysfunction looks like choice more often in ADHD-PI than in other presentations.
Open questions
Research still cannot follow the choice in real time
Most studies count fills or symptoms. Few capture what a person intended before a dose, what happened in the moment, and how the event was explained later.
Sources
The evidence behind this guide
Search by author, design, sample, topic, or year. The full report includes the expanded 35-source table and detailed caveats.